Using the tear down guide will help out a lot. Replacing rear camera lens covers is one of the easiest repairs you can complete on a phone. The hardest part will be getting the back cover off without breaking it. The trick is to use a lot of heat to loosen the adhesive. Use a thin pick to get under the back cover then slowly and carefully cut the adhesive holding on the back cover. Take you time and don’t rush while making sure the phone stays hot. After you have the back cover off use heat to loosen the adhesive holding the lens cover on. It should come loose from the back cover and you should then be able to replace it with a new one.