First, don't panic. A wobbly leg on outdoor furniture is usually a hardware, joint, or foot problem—not a reason to trash the whole set. Flip the piece over on a soft blanket or cardboard. Wiggle each leg to find where the movement starts: at the bolt, at the weld or joint, or at the floor contact.
If bolts are loose, tighten them. Use the right wrench or hex key. Tighten all bolts a little at a time in an X pattern. If a bolt spins or won't tighten, the hole may be stripped. For wood, wrap the threads with a few toothpicks and wood glue, or drill and glue in a dowel plug, then re-drill. For metal, use a slightly larger stainless bolt, a threaded insert, or an outdoor-rated epoxy or steel epoxy. Let it cure fully.
If the leg is loose at the frame, clean the joint, sand away rust or paint, and apply metal epoxy or outdoor construction adhesive. Clamp it overnight. For extra strength, add a small L-bracket or corner brace, then paint it to match.
If the leg is structurally fine but the piece still rocks, the problem may be uneven leg length or an uneven patio. This is common on urban balconies and concrete. Screw an adjustable leveling foot into the bottom of the leg, or add a heavy-duty rubber or nylon furniture glide. If you can't install one, use a stainless washer or outdoor shim under the short leg. Avoid stacking beer coasters; they won't survive rain.
If the leg is bent, try gentle pressure with a clamp or padded vise. For metal, a little heat can help, but don't cook the finish. If it's badly kinked, order just that leg from the manufacturer or a local metal shop. If the frame is welded, a mobile welder can often repair one joint for less than a new set.
Finally, replace rusted bolts with stainless steel hardware, add threadlocker to stop vibration loosening, and check the feet after storms or temperature swings. I've fixed several bistro tables and benches this way for under $20. Start with the simplest fix—tighten, level, and stabilize—and you'll usually save the piece.