M3U IPTV is a player app that does not provide its own channels or content.
To watch channels, you need to add an M3U playlist from your IPTV provider.
Used version 2 of the M3U IPTV app before?
You can import your last loaded playlist from Settings » Playlists » Add Playlist.
To switch back to the previous player, go to Settings » General » Switch to old app version 2.