If the "hostname" is "localhost" and you're connecting from a remote host (for example from your PC, while KMP is installed on a remote server), you would need to use the server domain address or IP.
If "hostname" may have an internal IP address (e.g. 127.*.*.* or 192.*.*.*) and if you're connecting from another network (which is external to the network with the KMP server), you would need to use the external IP of this server.
The MySQL server may have connection restrictions, so it is possible that you want be able to connect to it from you PC. Contact your server administrator to resolve this.
If you experience troubles with connection, it would be better to install HeidiSQL on the same server where KMP or MySQL server runs - in this case you will be surely able to connect. Though security restrictions in you company may not allow this.