Change completed status on assignment?

Summary

Supervisor erroneously submitted causing a "complete" status for his emps.

Content

A supervisor made an assignment to two of his employees - but mistakenly submitted it (thinking it was confirming the assignment).  Now the assignment is marked "complete", and the two employees are unable to access it. 

Is there a way to fix this?  

- Un assigning doesn't work because it's been submitted, 

- Re assigning doesn't work because it's been 'completed'. 

Thanks in advance -