Employee has retirement as of 6/30 and 7/1 non worker is present, and Want to add assignment

We have scenario where Employee has retirement as of 6/30 and 7/1 non worker is present. Now wants to add the assignment before 6/30.

So to do that we need to reverse the termination and then cancel the non-worker work relationship.

so when we try to cancel the non-worker work relationship system gives me error.

Note: Retiree enrollment is not present only active enrollment is present. Retirement life event is process.

How to handle this situation?