How to unplug backup sensor from bump in 2012 X5

[miamipanther]

While I am trying to remove the bumper to install hitch, I was stuck in the first step, I have spent 5 minutes and still couldn't figure out a way to unplug backup senor wire harness.

The backup senor wire harness has black body with a grey clip on side, I tried to push or use a screw to seperate them, no success so far. I didn't use brutal force since I was afarid to make permanent damage.

Did anyone have some experience? What's right way to unplug it without breaking it.
Thanks