Hey Olivia!
Letting people sign up for your site is a general WordPress sort of thing – i.e. it’s not specific to Community Events or The Events Calendar. So you should be able to enable it in general by going to Settings > General in your wp-admin.
Once there, click the “Anyone can register” checkbox and save your changes:

Now anyone can go to [yoursite.com]/wp-register.php and make an account on your site! 🙂
So you can share that link with people you would like to become Organizers, or on a page or in your site’s navigation menu, etc.
Now, if someone submits an event anonymously, and then signs up for an account later, there’s no way for WordPress to “know” that the anonymous person in the past was this newly-registered account’s person, so the event will not be linked to their account.
But as soon as someone has an account and then submits events, the events will be tied to them and they can manage those events that they submitted.
I hope this helps!
– George