I had thought about suggesting Tung oil. While I have lots of experience with Tung oil on wooden rifle stocks, I'm ignorant concerning Micarta.Tung oil or another drying oil tends to work well with Micarta handles that have the bead blasted/rough looking texture to them. The oil will harden and usually lasts pretty well, but you want to wash and clean them first like RIBob said!
The oil will also darken up the scales so they don't look as light/dusty looking.
Lots of folks become confused about Tung oil, often buying inferior grade(s). See for suggestions: https://woodnbits.com/vetted/best-tung-oil/