How to replace tail gate

anil ali all you really have to do is to disconnect all the electrical wiring going to the back door i.e. camera, rear wiper etc. Then remove the back door support on either side of the door. Finally remove the bolts that are holding the back door to the hinges. You do want to do all of these things with at least one other person to hold the door etc. It will get heavy. Since we do not know what your replacement door has as accessories and if you need to changes door panels etc. I attached this from the service manual Prius-Hood-Doors.pdf which should help. Let us know if you need anything more specific.