1. Restore a backup ( if you have one );
2. Add a new user in the SQL: MyPHPAdmin -> Select your DB -> Users -> Add new user. For the password ( because it is in the SQL style ), I suggest to install a new blank WordPress page on a subdomain ( different from your website source ), insert a simple password ( ex "123678" ) and save it. Next, go to MyPHPAdmin -> Select your DB -> Users -> and copy the password ( the password of the new wp user will be something like AB39XM2SK38FDS2Sm21OpX ... ). Next, go back to your first database ( where you have the issue ), add new user and in the field of password paste AB39XM2SK38FDS2Sm21OpX ( the 123678 password ). Click Save and try to login.
Good Luck