The best way to remove a deeper scratch from plastic is just how you would remove a deeper scratch from paint. You start by using a more aggressive polish (I have used Meguiar's Ultimate Compound for this purpose on gauges) followed by a fine polish to restore as much clarity as possible as it will remove any slight marring/haze left over from a more aggressive polish (I have used Menzerna po85rd, but an OTC option is Meguiar's Swirl-X).
Use a foam polishing pad and repeat any steps until you are happy. Try to only use a microfiber cloth on the gauges in the future to avoid this from happening again.
Edit: plasti-x is a good option but may not be aggressive enough to remove the scratch completely.