Sign up for HumanSignal Services at onboard.humansignal.com. Create a contributor account, not an organization account. If you accidentally start an organization account, sign up again at onboard.humansignal.com with a different email address if needed.
After you sign up, look for a verification email from Label Studio Enterprise. Check your spam or junk folder if it doesn't arrive, and mark it as not spam so future emails land in your inbox.