If you open a group for your students, you can activate this option in the settings.
Students can then - if they are members of the relevant group - select the group at the bottom of their pages and submit their pages or collections there for assessment.
If the option does not appear, you probably do not have the appropriate role. Please contact lehrservice@leuphana.de to obtain the role “Institute employee”.
Please check the group settings. A processing date may have been assigned there that lies in the past. This happens in particular with copied groups. Set the date to a time after the planned submission.