The wiring is held to the inner workings of the foot controller by two screws. The Bakelite body has a built in step that acts as a stress relief for the cord.
Depending on what the problem is you might be able to simply rewire the foot controller by snipping off a couple inches of wire and soldering on some ring connectors then reassembling it.
However ~ if the wire is the old aluminum it's best to replace the wire from the controller to the connector then on to the wall plug. The insulation on the aluminum wire tends to be crumbly and brittle.
There is only two contacts inside the foot controller that will need to be cleaned. If the ceramic part is in good shape there is no reason to replace the controller.
You can either buy a new power / foot controller cord set and put your controller on it, or if you have the screwed together connector you can simply replace the wire.
It's not that complicated.
Joe