Check For Deal Breakers
Make sure your bench can be restored to safe working order. The last thing you want is a bench that might collapse while you're lifting.
Check the support structure, which is usually made of squared-off metal tubes. If the metal itself is damaged, it's time to get a new bench. Even if you can weld, don't bet on the strength of the repair.
Look at the slat (the padded area). It's made of a piece of wood, some batting and a cover. If the wood itself is broken, you'll need to replace the slat.
Check for warping or bending. If the support structure or slat is warped, bent or out of shape you should replace your bench rather than try to repair it.
Examine the hinge, if applicable. If there is structural damage to the hinge, you need to replace the hinge or the entire bench.
Tighten the Attachments
Find out how the slat is attached to the support structure. Usually this will be via several bolts on the underside of the slat.
Check each bolt in turn, tightening it with the socket wrench.
Replace any bolts that are missing, rusted, stripped or broken.
Test the repaired bench for stability. If it wobbles, look again at the attachment and the supports.