There may be a case in which one of the cPanel user request you to provide access to Mysql remotely. You probably can't open MySql port 3306 on the server because that would lead to security risks. So in such case follow below steps -
Login to cPanel >> Remote Mysql >> Add remote server's IP address under Add access host >> Click Add host.
Step 2 :
Open mysql port for the remote IP address. To do this update below csf file (firewall) -
tcp|in|d=3306|s=x.x.x.x (Replace x.x.x.x with remote server IP)
Now, remote IP x.x.x.x will be able to access Mysql on your server.