Use your opening tool to open the latch that holds the power button flex cable in place.

Make sure you open the black part of the latch, I tried prying at the brown part thinking that would open it, it didn't. No harm done though.

Use your tweezers to take the old flex cable out and out the new one in, this can probably be done by hand but it takes a bit of precision.

Don't forget to put that latch back down! (and sorry about the blurry picture)