This article will show how Chat Topics work with the new Chat. You'll see that the new Chat has reorganized how things look while adding a lot of new tools and options.
Step 1: Tap the chat icon on the bottom navigation bar
Step 2: You'll have two tabs at the top. The first one is for 1-2-1 messages and the other tab is for Topics (Group Chats)
Step 3: You'll see a list of all the chat topics that you are currently a part of. To join another Topic group tap on the Pink chat bubble on the bottom right side.
Step 4: This will show you a list of Topic groups available to Join.