I really doubt it fell from the machine to land on your sewing plate. It had to drop from above and I looked all over my Brother machines and can't see an opening on the bottom of the top housing. You can open the face of the machine (where the needle bar is and usually light bulb( and check there easily, that would be the possible place for it to fall. Look at part number 26 on this diagram. .
https://millardsewing.com/product/xe6416201/