Yeah, that didn't go so well. And the old network has since recovered.
The channel name will remain as #rmrk!If you use an IRC client and connect to irc.rmrk.net: You don't need to do anything. Whenever your ISP's DNS updates, you'll automatically arrive at the new (old) network.
If you use the online webchat: Again, no action required.
If you use a registered nickname: Assuming you used the nick back on the old network too, it will still be active there. Otherwise, register your nickname as normal (/msg Nickserv register password email)
You can tell which network you're arriving at by the channel topics.