It's basically like wild shape, I have it set it up but I don't know how to add it as an action or modifier or something else. Can someone explain to me how to do it? Please and thank you :')

1. Make a copy of the Blood Hunter - Order of the Lycan subclass.
2. Look at how they set up the Hybrid Transformation subclass feature.
3. Get inspiration on how to implement changes to your character sheet based on shapeshifting/wild shape rules.
4. Bang your head against the wall trying to figure out how to do all of the little nitpicky things that need to be done to make it work.
5. Get a pencil and paper and just write it down.

There is no way to explain how to do it because every little change is dependent on what your homebrew race is, what the creature your turning into is, what shape changing rules you're going by. Everything involves changing modifiers or adding actions, with the caveat that you can't take away your normal race's actions thus making the character sheet confusing and convoluted. It is possible with enough duct tape and chicken wire to throw together something that could be passable or functional, but no where near publishable by any self respecting author.

EDIT: Also it's not possible to do some things. Take hit points for example. You can't change your hit points for the different creature you turn into and even if you could, there's no way to reset to your previous hit points after you revert back.