As a RM, PMO, I can release TMs
Resource Managers (RM) can select a team member in a resource pool to see his or her assignments to work packages. By clicking a project/package, RM can see assignment details at TEAM MEMBERS > ASSIGNMENTS

Click button [Release] to release this team member from this work package.
PMO can do the same operations as Resource Managers (RM) at tab TEAM MEMBERS:

Frequently Asked Questions
Who can release a team member from a work package?
Both Resource Managers (RM) and PMOs can release team members from work packages using the TEAM MEMBERS tab.
How do I release a team member from an assignment?
Select the team member from the resource pool, view assignment details under TEAM MEMBERS > ASSIGNMENTS, and click the [Release] button.