Remove the rns-e, take the lid of via 5 screws, dvd drive no doubt will be encased in a thin plastic housing, you can reach through this from the rear fan area iirc, get a cotton bud, dab it on your tongue, rub the laser head, probably be black when removed, dry of with other end of the bud, then test again, worked for me multiple times & others advised.
Dust/dirt builds up with the heat & sits on the head, so just needs a wipe, but dont go in hammer & tongs, just be gentle, slowly wipe, should be fine & dont put a huge dob of spit on end of bud lol.