In the first instance, wipe it with a cloth and warm water. Alternatively, clean it with a cotton bud. If dirt has lodged behind the knob, you can remove the knob, clean, and then replace the knob.
In the first instance, wipe it with a cloth and warm water. Alternatively, clean it with a cotton bud. If dirt has lodged behind the knob, you can remove the knob, clean, and then replace the knob.