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.