Look for the line where the backcover is snapped to the chassis and use a thin metal spudger to get between the cover and the chassis.

The backcover is quite flexible and sturdy but be careful with the three buttons - use your nails if possible.

The cover should come off really easily but beware as the fingerprint sensor is still connected to the motherboard - do not rip it off.

Use a heat gun to soften the glue and poke gently until the sensor is loose.