Go to the tab in your profile box listed as "Games."
Click the box next to the "wishlist" spot. Then type out games name. If for some reason it doesn't have an "add" option next to it. Add it to your wishlist, and then go to your wishlist and add it to your games.
Edit: for anybody else who
Thanks. Seems like some games are just not in the database. Trying to add "The Walking Dead" but can't find it.