Hello, first time poster at DIY,

My house currently has two 3-way switch controlling a light at the
downstairs entrance. I like to turn one of the 3-way switch located at
the lower floor to a motion sensor wall switch.

I opened up the existing 3-way switch box and it has 3 terminals with
3 wires (black, red, white), how do I hook it up to my motion sensor
switch which has 2 black wires and 1 green (ground wire)? My goal is
to make the top floor switch either an independent switch, or "3-way"
with the motion wall switch.

Any help is appreciated. Thanks.

Peter