Use the point of a spudger to lift up the locking tab on the power button cable ZIF connector.

The locking tab should be nearly vertical when unlocked. If it isn't, gently push the tab forward to compress the waterproofing gel and unlock the tab.

Use a pair of blunt nose tweezers to grip the cable close to the head and pull it away from its ZIF connector slowly and steadily to separate the coating.

During reassembly:

Inspect the head of the cable and the ZIF connector for any remaining coating that could prevent a good connection.

Peel off the coating—heating the cable and the ZIF connector when the coating becomes too brittle.

It doesn't have to look pretty! You just need to remove enough coating to have the cable sit properly in its connector.