If your Joy-Con’s SYNC button isn’t working, try these fixes. First, clean the button with compressed air—blow short bursts around the button to remove dust that’s causing it to stick. Use a cotton swab dampened with isopropyl alcohol (70%) to gently擦拭 around the button’s edges, dissolving any sticky residue. If cleaning doesn’t work, reset the Joy-Con by removing the battery (requires opening the Joy-Con with a tri-wing screwdriver)—wait 10 seconds, then reinsert the battery. Note: Opening the Joy-Con voids the warranty, so try official repair first. Update the Joy-Con firmware: attach it to the console, go to 'System Settings' > 'Controllers and Sensors' > 'Update Controllers'. If the SYNC button still fails, the internal switch may be faulty—contact Nintendo Support for repair, as this is often covered under the Joy-Con drift warranty.