Adding and withdrawing students from allocated assignments in teams

I have allocated assignments to students in Teams but have two issues.

Firstly, once I have allocated the assignment to students I cannot see how to withdraw them from that assignment eg a student suddenly discovers that had a credit for that particular unit and does not need to complete it.

Secondly,sometimes I have students enrolling late for the same group once I have allocated a unit assignment. I cannot find a way to add them to that assignment without having to create a new once specifically for them.

Help would be appreciated

Thanks

Ken