Replacing an electrical cord
Since it's a plug attached device, is not covered by code. However, you should still be concerned with safety while making the repair. 

The safest bet here, would be to completely replace the cord. This means locating where the existing cord connects to the couch, removing the old cord, and replacing it with a new one. 

You'll also want to find a cord that contains the same gauge wires as the original.  The existing cord should have writing on it, that should list the gauge (AWG).

As to where to buy a cord, that's going to depend on where you live.  You may be able to order a replacement from the manufacturer, or possibly locate one on Amazon.