Hey, I'm new to itch, but this is the first link that google gave me
https://itch.io/t/808186/how-i-can-add-new-games-to-my-library-and-make-new-coll...
Its one way, but more handy way imho is to add "download or claim" button just like here https://itch.io/s/59311/free-food
Dunno how ot add it, but maybe you'll find it