There is a square hole on the underside of the spout closest to the tile wall but there is a white plastic piece blocking what I think might be the screw that needs to be undone to remove the spout. How do I get past this plastic piece? I can't seem to find any answer and need some help! Please and thank you!

Did you twist the spout? Pry the plastic piece out and see if there isn't a Allen Set Screw up there. '
Take a knife and scrape the spout. Is it plastic or brass under the chrome finish. Let me know what you find, Tom