Free user vs Free trial

Hi, I'm a licensed user that created a sheet and invited maybe 20 people to share the sheet. These are people who had never seen a Smartsheet before. Some of the people signed up for a free 30-day trial instead of just signing up as a free user to collaborate on my sheet, the latter of which is what their intention was. I don't know what the email looked like on their end so I wasn't able to advise them how to sign up.

Now they're getting notices that their free trial is ending in 10 days. How do they pivot from a free trial to just a free collaborator on the sheets I create?