Also when u unlink the account already paired with hes steam id do he need to create a new factorio account?

So the ID is my steam 64 id right? Alright

So, my brother bought the game to play with me, but before i used to play on the pc he uses now so my Factorio username was there when he installed the game. Now he tried to make a account with the email used on his steam account and tried to logg in but then it said, Steam ID already paired with ...