You can use Google Draw or Google Slides to insert an image file, and then use the "curve" line tool to create an enclosed shape (filled in with green!) wherever you want to create a window for your face!
The "curve" line tool in Google Draw + Slides allows you to click around an object to create irregular enclosed shapes filled with color.
Then, export your image as .png, and import into WeVideo
The video of you speaking goes UNDER the still image. Use the color keying option in the clip editor to remove the green and make it transparent.