How to change block heater cord

Do you have the new parts to look at? If you have an aftermarket heater, most of them have cords that just plug into the heater, and replacement is pretty obvious. Pull the old one out and plug the new one in. The metal clip that holds the heater in corrodes and fails more often than the cords so if you bought a whole new heater assembly and just use the cord, you will have a spare heater.