There are a couple of ways to get more learners to join your sessions:
Schedule your sessions at least a week in advance to allow more time for learners to register
Whether you are a new or current tutor, you want to consistently host sessions and offer lots of engagement. As you dedicate more time to tutoring and do it more consistently, you will gain more credibility and learners will register more for your sessions
Community engagement sessions also gain a lot more learners
While the self-promotion of sessions/series is not allowed, you can still mention your sessions in some channels, when appropriate. Examples include:
Sharing your session under someone's introduction if there's alignment
For instance, if a learner mentions in the introductions channel that they want to learn US History, and you're already running a series on US History, feel free to welcome them and mention that you have a series on that topic/share the link)
Looking for co-hosts in the tutor channel
Asking learners in the discussion channel what types of topics/sessions they would be interested in