If you need to assign a new user to a cPanel database, follow this guide.
How to assign a new user to a cPanel database
Login to your Client Dashboard account
Click on My Services button in the Welcome page
Click on manage service button
Login to cPanel link on the sidebar menu
Scroll down the page until the databases tab
Click on MySQL Databases
Click Jump to MySQL Users in the top right corner of the page
Under Add New User, enter a username and a password. Retype the password in the Password (Again) field, then click on Create User
Scroll down the page and you will be able to add the user to the database you want. First, select the user, then choose the desired database and click on Add.