You can find this example already in your Mirror Project, location: Assets/Mirror/Examples/EdgegapLobby
This is a copy of the Tanks example (basic scene with player controlled tanks), but with a lobby ui for using Edgegap's Lobby and Relay service.
It showcases how one might interact with the EdgegapLobbyKcpTransport to list, join and create lobbies, providing a good starting point for anyone wanting to use Edgegap lobbies.