Also, to manage your databases, you need to use the pre-installed phpMyAdmin instance. Using other database management systems on our hosting system may result in an error doing what you want to do.
The server “Localhost MySQL” is not correct. I’m not sure what the dropdown has as options, but there should be a way to enter a custom database hostname or IP address there. The value to use for that can be found in the control panel (it looks like sql123.epizy.com).
The best solution I can offer you is to get rid of that useless mess and use something that does support the absolute minimum of database connection configuration.
It’s very normal to operate a database on a different location than localhost on the default port. The fact that they clearly omitted to provide a few input fields for such basic settings and hard coded these details is a stupid design error on their end.
I highly recommend to use something else instead, like phpMyAdmin or Adminer.