key pad

If the tracks are exposed, you might be able to use an electrically conductive epoxy to reconnect the traces. You might need a microscope to be sure you don't short across two tracks.

If the tracks are covered with an overlay, you'll have to find a way to expose enough of the track to effect the repair.

Spot on advice.

Copper tape comes in very small sizes, as does wire. Tricky, but never impossible.

They also make what are called conductive trace pens. These use a silver based ink. Be sure to use a mask to prevent shorting.

If the ribbon traces are just scratched this should work. If the ribbon is cut you will need to fix the area cut first as the ink will tend to flow along the cut.

Either way to will need to immobilize the section from movement or vibration to prevent future failure.

If it is not a very special keyboard then it's not worth fixing it, the conductive pen will cost you 26 to 38 dollars !!

But you can get it here if you wish:

Conductive pen

Sometime you can fix it with a pencil. Redraw the line with a soft pencil like 2B.