Chosen Solution
Just got the iPhone battery replacement kit and I took off the top part of the phone and I started to take the screws off on the battery cover. The left come out easy but the right won’t move at all
Either the head is stripped (your screwdriver is sliding around inside the screw head) or the threading is stripped (the screw is spinning but not going anywhere). If the former, use a tiny flathead screwdriver to get some leverage on the screw. If the latter, slip a razor blade tip or Xacto blade edge under the head and lift up as you unscrew it.