There is not a release for the stab-in connector of the quick wire backplate, however, you can easily remove wires with the following technique. Always make sure the breaker is off before handling wiring.

Grasp the wire with pliers

Lineman pliers work great, but needle nose or other pliers will work as well.

Apply gentle pulling pressure on the wire while rotating it slightly back and forth. This combination of forces will walk the wire out of the connector. Very little force is needed; it is almost entirely technique.

You won't need to rotate it much, or pull very hard. Just be gentle and apply this technique for a few seconds, the wire will come right out.