grab the the odd shaped tool (in tool box next to little laser)
acetone
Q-tips
microfiber towel/blue paper towels
unscrew the back plate holding in the mirror being careful not to drop it once its open
NOTE: taking the mirrors out shouldn't mess with the alignment if you are carful enough, but should check it after wards just in case.
start with using a q-tip and acetone to softly clean the surface until nothing is on the q-tip
use the microfiber towel to get off any remaining dust or debris
reinsert the mirror into its slot and slowly tighten it