Homebrew subclass question

So I'm trying to add extra damage to unarmed attacks that increase when you level up but I can't find where to do that in the creation pages. Does anyone know where that is or how I can find it

That depends on precisely what you’re trying to accomplish.

1. Are you trying to add a fixed number to the already existing Unarmed Strikes?
2. Are you trying to add an additional die to the preexisting Unarmed Strikes?
3. Are you creating your own Unarmed Attacks?

I'm trying to add a fix number to unarmed strikes that go up when you level up

You have to create a feature at each of the levels when the damage is sposta increase, and attach the following Modifier to each of those features:

Modifier: Damage->Subtype: Unarmed Attacks->Fixed Value: X

Thanks, and X is the number added

Correct.

And where about do I need to put that into?

You create a subclass feature at the appropriate level, and then add that Modifier to it.