Turn the couch over so the bottom is facing up. This allows you to access the springs from underneath the sofa.
Pry out any staples holding the fabric under the couch to the frame with a screwdriver or needle nose pliers. Don't worry if the fabric tears because it is simple to replace when necessary.
Locate the damaged spring once the fabric is off the underside of the couch. If you have trouble locating it, take the cushions off the top of the couch and feel for the damaged spring from there. This helps you find the right one from the bottom.
Reach into the couch from the bottom and bend the damaged spring with your pliers. Manipulate the spring until its shape matches that of the springs around it as closely as possible. If the spring has broken off of a bracket, repair the bracket by nailing it back into the couch frame with a hammer slightly over from where it had previously dislodged. Use a replacement bracket if necessary and slide the spring back into it.
Staple the fabric back onto the bottom of the couch by inserting the staples into the frame with a construction stapler.
Turn the couch back over and replace the cushions.