I removed a participant from a recurring meeting, I want to reinstate them, how can I do this?

When a user is removed from a meeting, that ban from the meeting is only temporary and only applies to that ongoing session. As soon as the session ends, the ban is lifted and they can join the next session, whether that starts 5 minutes or a week later. 

Hope that helps and please make sure to mark the solution as accepted if this information is what you needed.