How should I fix a damaged extension cord end?

Cut off the damaged end and install a new male or female plug. Match the replacement plug to your cord’s gauge (16 or 14 gauge for most household cords). Strip ⅜ inch of insulation, connect the hot wire to the brass screw, neutral to silver, and ground to green. Tighten securely, tug-test each wire, and close the housing. If the cord is frayed beyond the last few inches, replace the whole cord—don’t rely on electrical tape.