Ah okay. There is an easier way, you can copy-paste the address into the search box on Mastodon. This will bring up the group's profile and you can just click "follow". (There are instructions for this on fedi.directory, in the link at the top saying "how to use this site".)
I'd normally just do a long list of accounts to follow over on @FediFollows so that you don't have to do this. However, in this particular case it would spam all of the group members of all the groups