Use the pointed end of a spudger to depress the metal tab on the side of the power button cable's board connector.

With the metal tab depressed, use a pair of tweezers to pull up on the pull tab to disconnect the power button cable from the center chassis.

Pull only on the pull tab, not the cable itself.

Don't pull on the cable without depressing the metal tab, otherwise you risk damaging either the cable or the connector.

During reassembly, the cable should lightly "snap" into place when inserted.