I am trying to set this using modifiers for versatile weapon, but it will just not work at all. Is there a trick on how to do this properly? 

I want to create Spiked chains with the following properties: 

Spiked chains were a length of metal chain whose last few links on each end were enlarged and enhanced with spikes. The length and size of these links were usually proportional to the size of their wielder in order to ensure optimal performance.

Damage: 1d4
Damage Type:Piercing
Item Rarity: Common
Properties: Versatile(2d4), Finnesse, Reach

- The spiked chain is a melee weapon in the flail weapon group.
- A spiked chain has reach, so a character wielding
it can make attacks other than opportunity attacks
on enemies either 5 or 10 feet away.
- As a bonus action after hitting with this weapon, you may perform a trip attack. Dex save dc 10 + proficiency bonus.

Í cant really find a way to change versatile dmg to 2d4 

Link to Item: https://www.dndbeyond.com/magic-items/6602791-spiked-chain

Thank you 

You must open modifiers  and type in > Damage > Damage Type Piercing> Die > 2d4.

But that will set all your attacks for the dice damage to only 2d4, as of now it is impossible to fully have a separate tab for the damage die of versatile weapons.

Unfortunately this isn't possible; while we can add the versatile weapon property we have no way to specify the damage in brackets (it's always just one die size higher, so on a d4 weapon you'd get a d6).

One way you could do this is to create a second item, e.g- "Spiked Chain (2-hand)" with the Weapon Property -> two-handed modifier, and also Damage -> Piercing (1d4), don't forget to override its weight to 0.0 (under additional information). This way the player can add both and just roll the correct one (though sadly the D&D Beyond dice roller currently won't roll the extra damage automatically, so it's purely for informational purposes).

Not sure why the Weapon Property -> Versatile modifier can't just use the dice fields to set the 2-handed damage dice, it would make things a lot easier.

Quote from Haravikk >>

Unfortunately this isn't possible; while we can add the versatile weapon property we have no way to specify the damage in brackets (it's always just one die size higher, so on a d4 weapon you'd get a d6).

One way you could do this is to create a second item, e.g- "Spiked Chain (2-hand)" with the Weapon Property -> two-handed modifier, and also Damage -> Piercing (1d4), don't forget to override its weight to 0.0 (under additional information). This way the player can add both and just roll the correct one (though sadly the D&D Beyond dice roller currently won't roll the extra damage automatically, so it's purely for informational purposes).

Not sure why the Weapon Property -> Versatile modifier can't just use the dice fields to set the 2-handed damage dice, it would make things a lot easier.

You could modify a Double-Bladed Scimitar, change the damage type to piercing damage. You would probably want to add a note to ignore the Special from the text description since that is something that cannot be removed. Check out the thread Everything you need to know about creating Homebrew Weapons.

Thank you everyone!