The official HCoop IRC channel is #hcoop on Libera Chat. It is also bridged to XMPP discuss@conference.hcoop.net (coop members only) and Matrix #hcoop:matrix.org (unofficial).
You can find an introduction to Internet Relay Chat and more at IRChelp.org, and information on using Libera Chat specifically in their Guides. You should consider registering an account if you use IRC regularly, although that's an optional step as #hcoop currently doesn't require registration to join.
There are a couple alternative ways to access the IRC channel without using an ordinary IRC client:
There is a web interface for the chat at https://web.libera.chat/#hcoop.
There is a Matrix bridge available for testing, though it's not yet officially supported. The Matrix address for the channel is #hcoop:matrix.org. If you join via Matrix, you'll be invited to chat with an appservice bot in a "bridge status" room; among other features, it can store your IRC nick and password for future sessions. (For initial account registration, it's recommended that you use Libera's web chat interface to avoid any possible problems with Matrix federation.)
There is an XMPP (aka "Jabber") bridge hosted via cheogram.com to the discuss@conference.hcoop.net XMPP Multi User Chat (MUC). That allows users to join the discussion from a desktop client such as Dino or a mobile client such as Conversations (also available on F-Droid). Members may connect with their hcoop credentials; your username (or JID) includes @hcoop.net.
Like most IRC channels, ours is not especially "on-topic," but it's a great place to get advice about using your HCoop account. Please join and "idle" there if you can to help build momentum and answer other members' questions!
Our volunteer admins don't treat IRC as an official support method, because it is way too hard to organize handling of support requests that come over such an unstructured medium. This means that you're free to ask questions or make requests that can only be answered/fulfilled by admins, but that they won't feel obligated to reply. Open a support ticket on the portal for such issues.