Antonym to 'Assign'

What about "dissociate" or "deallocate"?

There is some question about whether it is a real word, but I have seen and occasionally used "deassign."

If you "assign" users to an operator, you may "remove" users from the operator.

Divest comes to my mind:

(transitive) To strip, deprive, or dispossess (someone) of something (such as a right, passion, privilege, or prejudice).

You shall never divest me of my right to free speech.

So if the original procedure is:

Assign users to an operator.

The antonym is:

Divest an operator of users.

You can revoke a task that has been allocated to someone