Hi itpromotion,
You’d need some means of tracking them which might be a matter of capturing their user ID (using get_current_user_ID() or a similar function, if this is limited to authenticated users) and storing a record of this in the database somewhere. Then, of course, you’d need to retrieve that record of users and output it.
It’s not something that is facilitated out-of-the-box by The Events Calendar, though, so really you would either have to build something yourself or perhaps research and use a suitable existing plugin.
Hope that helps!