MySQL comes with a default user account called 'root', initially it has not password set.
So on the phpMyAdmin login page use
Username = root
Password = blank (dont put anything in here )
You are now logged in as the SuperUser and can do anythng.
So now make sure you set the same password on all 3 root users that exists.
Thats
root@127.0.0.1root@::1
root@localhost
AND DONT FORGET THE PASSWORD!!!!! Its a pain getting back in if you do.