So I wanted to reward my parties fighter with a war hammer that would give them the ability to use a 3rd level eldritch smite twice per long rest, but couldn't figure out how to build it in homebrew creator. The closest I could find were the regular smite spells, am I looking in the wrong place? Does anyone know how to do it? Thank you in advance. 

Make a custom action for the smite damage. When you smite, you can just click that extra damage after clicking the normal weapon damage.

I haz video.

Actions such as that cannot be added to magic items at the current time. You have two options:

1. Create an “Eldritch Smite Spell” just for this magic item and add it to the item with two charges. This will still not make it automatically rollable on the character sheet though, the player will have to roll it separately.
2. List it as plain text and add the 2 charges, but let the player implement the smites as custom actions directly on their character sheet as Cyb3rM1nd suggests.