Stuck plunger

The plunger on the TLA-55 rotor is stuck and does not disengage upon depressing it. Earlier the o-ring on the lid had come off during the operation of the instrument. The rotor had stopped spinning due to vacuum issues once the o-ring flew off. How can I disengage the rotor? The instrument is Optima TLX.

Equipment: Beckman Coulter Optima TLX