How to clean the PS4 optical drive?

I recently found 2 PS4 game discs with scratches consecutively.But I always handle them very carefully.I just took them out of the disc cases and put them into the disc drive or the other way around.I wonder if there are something got into the drive and causing these scratches.So I'm trying to clean the optical drive but don't know how and can't find a video showing this.Could someone help me with this?Or you have the same experience and know its another reason causing this?I appreciate your help.