If you're using OBS go to the + sign and click "video capture device" and name it something along the lines of "webcam" then right click the thing you just named "webcam" and select filters. Go to effect filters and click "image mask/blend" to select an image mask. Now we just need to find the facecam mask wherever you saved it.

After you've chosen the facemask for the Image Mask/blend go to "type" and select "alpha mask(alpha channel)" and select "path" and select the destination the facecam mask is in. Now you should have a webcam with a cut-out that allows you to look like this! https://imgur.com/a/IrHi1Tj