IScrews can help you. It has a layout with a printed iPhone on top and holes to put the screws in the right position as you remove them. Available in versions for iPhone 3G, 3GS, iPhone 4, 4S, iPhone 5, 5S, 5C,iPhone 6/6+/6S/6S+, iphone 7/7+/8/8+ and iPhone X/XS/XS Max/XR.
eBay