You completely follow this tutorial: Replacing the rear camera of the iPhone SE
At the end of it, you put your phone on the screen side (there is no screen at this time) then, you heat the camera window on the outside and with the help of a screwdriver pushes the glass inwards.
Attention it can go quickly so, if you do not want to take the risk also remove the motherboard.
FYI, I heat at about 300 ° C with my hot air station.
After for the nipples, there are two small holes on the optical side of the camera on the metal element if you remember more.