1/ They need to be taken apart, thoroughly brushed and rinsed with distilled water to dilute and disperse all the chlorine, then brushed and rinsed in a 99% isopropyl alcohol bath to displace the distilled water. This, you can do. Use a soft toothbrush for the brushing.
2/ If there are traces of corrosion and dullness, those solder joints should be reflowed. Badly damaged components may need replacement. This, however, must be trusted to someone with soldering or micro soldering skills.
After step 1, you could test and if your are lucky and they are working, you can skip step 2.
If they have a rechargeable battery, it could have died and may need replacement.
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Finally, once opened, and depending on the type of sweat proofing they have, they may cease to be sweat proof anymore.
1/ They need to be taken apart, thoroughly brushed and rinsed with distilled water to dilute and disperse all the chlorine, then brushed and rinsed in a 99% isopropyl alcohol bath to displace the distilled water. This, you can do. Use a soft toothbrush for the brushing.
2/ If there are traces of corrosion and dullness, those solder joints should be reflowed. Badly damaged components may need replacement. This, however, must be trusted to someone with soldering or micro soldering skills.
After step 1, you could test and if your are lucky and they are working, you can skip step 2.
If they have a rechargeable battery, it could have died and may need replacement.