Remove the battery, then squirt some rubbing alcohol underneath the dial (wet a cotton ball with the alcohol, then squeeze it out inbetween the dial and the camera body, or use a syringe), or use a spray can of electronic contact cleaner. To make sure the rubbing alcohol gets in there, you can widen the gap between the dial and the camera body by inserting a fingernail inbetween, but don’t overdo it or else something might break. Once you’ve got the rubbing alcohol in there, rotate the dial a bunch of times to work the alcohol inbetween the metal contacts inside the dial mechanism to clean off what seems to be oxidation on those contacts. Apparently the contacts oxidize quickly—maybe the manufacturer “forgot” to apply a gold surface layer to them. After you squirt in the rubbing alcohol, wait about fifteen minutes before you reinstall the battery, to let the water in the rubbing alcohol evaporate, or else it might short out some electronics inside the camera and fry it. Preferably use 91% rubbing alcohol instead of 70%, since 91% will introduce less water into the camera. This process works for many people, but not everyone; when it does work, it might be only temporary for some people, at which point you can do it again.