Apparently it’s done like this:

Pinch the two links next to the Powerlink together so that the Powerlink bulges up.

Pinch the side plates of the power link together.

Push the links adjacent to the Powerlink toward each other. You should see the pins move into the inner hole.

Pins come out and the Powerlink comes apart.

I had great success when they were new-ish, but time and grit has made it a bit harder to get to work, hence re-checking the instructions…