I'm trying to change the spells these homebrew get but it only gives them the underdark. I made a copy of underdark to have a based made how do I change the spell they get do I need to add them in at each lvl they gain them? Or do I just modify one of the list shown?

You do it here:

The list in the class feature is just cosmetic. It still needs to be updated with the new spell list so everything matches for the user, but the actual mechanic is handled under “Basic Information” for the whole subclass.

Ok, I see now. thank you so much I have been trying to figure that out for so long!!