So I’m the DM for a game, and I had a player who said he’d want to be a warlock. I say ok even though this isn’t Eberron and I ask what class. Warlock. I’m helping him character since he’s a little new. How would I help him tie his race/class combination into a way that makes sense?

Whats the patron, because they may want different things. Only a fiend would want a soul I think, and not even all of them. And warforged still might be able to give their souls away, who knows.

Hexblade

Well that should be easy. A hexblade is just a sentient weapon that grants powers. People will typically start their characters having their patron in hand, but that's a popular house rule I believe. They can get powers from an encounter and deal, or like many patrons, you may have not seen them but have spoken with them.

An idea for a warforged hexblade could be that during a battle, he took down the person that was wielding his patron, and took them for himself, becoming a warlock, or maybe someone that dabbled in sentient creations made the weapon and the warforged, which could be a cool twist.

Ok,  might actually use your first idea. I like it and I bet my pc may like the idea as well

I play a warforged warlock; the DM just opened a portal and brought me to her world. The character has incomplete memories of the past. Feel free to ask me questions. I took Mask of Many Faces at the first opportunity, so I would blend in to the local populace better.

Maybe a Dororo style character who wants to get their physical body back by killing several creatures or doing tasks for it? Or maybe the patron place that soul in a body to do it's bidding or as a part of the bargain.

Many strange things happened during the Mourning, the cataclysmic event that destroyed what was once Cyre.

You were but a soldier fighting on the battlefield that day when a blast of magic destroyed your entire company.

You escaped with nothing but your life and your sword.

And now the sword whispers to you...

Could literally have any patron you wanted. Whos to say the patron didnt build the warforged in the first place?

I played a warforged where I flavored their warlock powers as subsystems coming back online after it was ripped out of ebberon by *insert plot point here* otherwise warforged would work like any other race (it's left to the DM if they have a soul the same way as other races)

I like the idea of the new Genie Patron option and that perhaps the Warforged had once been tasked by a lord or someone who obtained a Genie vessel to be the bearer or protector of the vessel. Then, once the lord was betrayed by the Genie it set the Warforged free. With nowhere to go the Genie offers a pact to the Warforged as a way of showing gratitude for their years of faithful service. 

Now the Warforged makes its own way in the world, traveling and adventuring in order to seek out its own fate carrying with it the Genie Patron’s former vessel, using it as its spell caster focus. I like the “ring” option for this purpose and the idea that the Warforged has it somehow integrated into its breastplate.

I made a Warforged hexblade warlock. Here's a summary of his backstory to help spark some ideas:

Chisel was originally made to assist a carpenter's guild. His creator eventually grew old and senile. In a fit of insanity, they installed a strange crystal that they found in some ancient ruins into Chisel's chest, then shut him down and sunk him to the bottom of a nearby lake. Chisel eventually* reactivated and realized that he could channel some new abilities through this crystal. It allows him to reconfigure parts of himself to cast spells and use his warlock features. As an example, his eldritch blast fired out of his palm, and his pact weapon would be summoned out the gem on his chest (Similar to Steven Universe if you've seen that). When he casts shield, the panels on his arm sort of unfold into a shield, that projects a barrier (Similar to Reinhardt/Brigette from overwatch). I drew heavy inspirations from the Gurren Lagann mechs and Iron man's suits for this.
Chisel technically didn't make a deal, nor was he even fully aware that he was a warlock. I planned for him to slowly learn this. His patron would likely be an AI or soul or something within the gem itself, or the gem would be providing a link of sorts to the patron. I wanted to leave some of the details up to the DM.

 *This campaign didn't last long, so I never really decided how long he was out. I was thinking it would be a somewhere between 100-200 years.

I have a Hexblade warlock in a homebrew world where all spell casting comes from relics left behind by avatars of the gods. In my case, the relic in question was a sword and when crafting the warforged they melted the sword down and used the metal from it and the gems for his construction and eyes. So he literally has the voice "inside" his head.  It also means that there are times he exhibits a distinctly different personality from his more detatched Warforged one, when his patron has a particular interest in what they are doing.

Overall incredibly fun to play!

I’m playing a warforged warlock who believes their maker an artificer is their patron, who has tasked them with finding treasure. In reality the artificer has tasked them with finding scraps, trinkets, and magical oddities which they can add to their collection. The artificer sends mechanical upgrades to the warforged periodically which they view as pact boons as they level up. We had to homebrew the patron and choose the spells that made sense for their mechanical nature, but it’s been a fun character to play