If you are on Windows, the file is in your user's AppData folder, usually "C:\Users\<>\AppData\Roaming\mediterraneancoin"

You can open folder by using Windows start menu and typing %appdata% (including percent signs) which will open file explorer on default AppData folder, and then going into "mediterraneancoin" folder.

Config file name is "mediterraneancoin.conf".  If file does not exist, create new text file, rename it (including extension, Windows will complain, say yes), and paste the "addnode" lines.  Save config file and restart wallet.  When it starts to sync, it may take quite a while to load two years of blockchain.

Sorry I don't know where the config file is on Linux, should be somewhere in your user's home folder too.