It is possible to access a database with phpMyAdmin without going though Control Panel.
You may need to ask the host for details on how to do that with your server and get an access link.
The other person will of course need the username and password for the database.
That depends on what you have set up for the database.
You could use Cpanel to create a DB user account just for that person. That would give you the most control over their access.
With the database user that the other programmer will be using make sure that they only have permssion to do/acess just what they need to do their job, nothing more. For example if the database has 20 tables and they only need to access 5 of them, they should have no rights or permissions for the other 25 tables. If they don’t need to delete records, don’t give the database user permission. You’ll probably want to deny them the ability to make any changes to the structure of the database or to truncate a given table