Enable users to undelete their own files

This isn't possible I'm afraid, normal users cannot see deleted objects or undelete them. This always requires administrative rights. Normal users need to ask an admin user to undelete their documents if they deleted something by mistake.

User guide: Deleting, Undeleting, and Destroying Objects

Thank you for the update. Still, having the option to enable it on individual basis would reduce IT support workload. Please take it as a suggestion then.

Thanks for the feedback. Note also that you can remove the delete permission from users via the object permissions if you want to avoid these situations and only allow certain users / user groups to delete certain types of documents.