Hello there. 
You just need to download WeMod: https://www.wemod.com/
And then use the Assassin’s Creed Unity trainer that we already have for the game, depending on which store you bought the game from:
- Steam: Assassin's Creed Unity Cheats and Trainer for Steam
- Origin: Assassin's Creed Unity Cheats and Trainer for Origin
Then activate whatever character cheats you want while playing the game.
You are very welcome. You can give us money to support the development of this software by purchasing Pro here: https://www.wemod.com/account/billing. Thank you. 