How can users come back to complete a form later?

Yes, users can save forms and continue later. Refer to the guides below:

For default Layout Forms: https://www.jotform.com/help/97-How-to-Save-Forms-and-Continue-Later

For Card Layout Forms: https://www.jotform.com/help/495-Setting-up-the-Continue-Forms-Later-Feature-in-Card-Forms

For further assistance, do let us know.