Hi Nicholas, thanks a lot for you replying. But I am still confused on how to do it. I have been trying to insert the mask, but it does not work.
I can add the mask on the “Color Correction”, but it does not let me to do it at Keying effect.



If I go to the mask effect and insert it, and insert the keyer. The keyer will still apply over the whole scene.

I have tried a lot of possibilities.
thanks!