You can just put the IP address of the server as the hostname.
Make sure that
The mysql server is listening on the public IP, so in
my.cnf
:bind-address = 0.0.0.0
The user you configured on the mysql server is permitted to access the schema remotely:
GRANT ALL PRIVILEGES TO `user`@% ...
To be more secure, you don't have to use the wildcard, you can use a specific host or IP pattern.