I highly suggest to not use root to login to your MySQL.
You are either using the wrong password for admin and/or admin does not have rights to access your specific database. Change/check your credentials in MySQL
Depends on if you use a console to interact with MySQL or a tool (and which tool). Best is to Google how to check and maybe change them for your method.
So I should change my username/password to something other than root/root
phpMyAdmin certainly has a password, it just authenticates against your MySQL server. So that’s not going to help him with a password that he doesn’t know.
Reinstall MySQL and remember the password you use on setup. Or if you didn’t use one, try root/root or root/(blank) to login.