Once a MySQL user is created, they will need to be given permission to access any databases that they wish to access. To accomplish this, you must grant the user's permissions to a database.
1 To access the MySQL Account Maintenance Menu, click on the icon above the words MySQL Databases on the main screen of your cPanel interface.
2 Select the user (the user will appear as mainuser_user) you wish to grant permissions for from the drop box next to User:
3 Select the database (the database will appear as mainuser_database) you wish to give that user access to from the drop box next to Db:
4 Select any privileges (abilities to modify the database) you wish the user to have by checking the box next to the privilege's name.
5 Click on Add User to Db to give the user permission to access the database.
The user will only have permission to change things you have given them the privileges for. Make sure the user has privileges for everything they need to modify.