Replacement of rear bumper parking sensor (how to?)

[Tahoe Dave]

I have been advised, by our local dealer, that the right rear outer parking sensor has thrown a fault code. This is the sensor above the tail pipe and I can (barley) get my hand on it. The sensors work in the front, however, when I put the Sport in reverse, the light on the dash blinks continuously.

I was wondering if anyone out there could guide me through the removal and replacement of the sensor.

Thanks in advance for your help...