I use the point of the tweezers to brush away any dirt from the center contact inside the button housing.

I do the same with the back side of the metal disc.

Finally, I use an air can to blow away any loose debris from inside the button housing. Be careful not to blow away the button plunger.

Sometimes, you might see an interior with significant corrosion. You may need to use a cotton swab with isopropyl alcohol or similar fluid to clean the contacts and disc. Just make sure the parts are dry before reassembling.