What Apps are good for adding effects to a voice recording for a horror Roblox game Fan Project?

I'm a Newbie VA but I'm working with someone doing a Fan Roblox Project based on Piggy called "Rise of the Lost Book" and I'm doing Voices for some of the Zombie characters but as far as I know we don't really have anything for adding effects to our Voices for the characters does anyone have any suggestions for what App I should look for that might help us out? Preferably a free App but I'll be good with whatever honestly.