I'm making an origin feat for one my homebrew background and I can't figure out how to make this benefit.

Keen Observer. Choose one of the following skills: Insight, Investigation, or Perception, you gain proficiency with it.

Any help would be greatly appreciated.

You can just add an origin feat on the character sheet by going to manage feats, you don't have to mess around with the backgrounds to do it  https://routerlogin.uno/

This is homebrew origin feat I'm making for Homebrew background. I'm asking how to add the choice for the three skills for the benefit I wrote down.