I disagree with this. If the snake's owner doesn't know for sure that the snake has a retained eyecap, it could be very dangerous to the snake's eye to try and remove it, especially with so many people recommending tape to do it (which I disagree with even more). Also, the scale around the edge of the eye is separate from the eyecap, and can be retained if the eyecap isn't. You CAN very gently wipe with a wet washcloth to see if it comes off, but I wouldn't take it any further than that. It won't hurt anything and should come off the next shed (same with an eyecap).
Steve