You will need to activate Attempts reopened in the assignment settings.
Do not use restrict access groups to manage resubmissions as students can see which students are members of each group.
Please note that in the vast majority of cases you will want to reopen attempts Manually. There are very few circumstances in which Automatically until pass would be used.
You will need to activate Attempts reopened in the assignment settings.
The Lecturer or Programme Administrator has to reopen the assignment for the student.
The student will now be able to resubmit their assignment, but only up to the cut-off date in the assignment (if set). If your resubmissions are due after the cut-off date you will need to use the grant an extension function to enable the students to resubmit.
In this case the assignment automatically reopens until the student reaches the passing grade which has been set by the lecturer in the assignment. This can be enabled by:
In Moodle 3.9, Turn editing on. Scroll to the relevant assignment and then select Edit and choose Edit settings.