On SnapI blocked someone, unblocked them and I want to add them again but I forgot their username. Is there anything I can do? Does snap have a list of like my former friends or people I’ve blocked?

There is no list of people you had blocked formerly, however you should have seen their username when unblocking them? That's the only way I can think to find their user. Maybe if you have a friend who knows their username, you can get it that way. Or if you remember just a bit of it or their first/last name, you can try searching that.