Purchase new garage door extension springs.
How to fix a garage door extension spring.
The new spring s diameter length and wire size or gauge must be the same as your old spring.
Loosen the unbroken spring.
Clamp a locking pliers or a c clamp to the track just above one of the rollers.
The easiest way to do this is to take the broken spring to a local garage door dealer or home improvement center so they can help you find an exact match.
Wipe off any excess then repeat the process on the other side.
Shove a winding bar into a bottom hole of the winding cone of the good spring.
Spray each spring with garage door lubricant.
Slide a grocery bag or piece of cardboard behind the spring to protect the garage door.