Replace it. But here's how to fix it if you must.

Probably not worth your time, but yes, you can repair a cut extension cord.

The safest and easiest way: cut out the damaged section and install a new male or female plug end. You can buy plug ends at any hardware store for a few bucks. Strip the wires, screw them into the terminals, done. This works if the damage is near one end.

If the cut is in the middle of the cord and you really want to splice it, get a waterproof junction box or an inline plug kit. Don’t just twist wires together and electrical tape it — that’s a fire waiting to happen. A proper inline splice uses screw terminals or crimped connectors inside a sealed box.

But honestly? If it’s a cheap extension cord, just throw it away and buy a new one. Splicing takes time, tools, and a bit of know-how. A new 50-foot cord costs $15-$20.