I did a search of the Singer site. When you request a manual for the 93220, they tell you to use the manual from a model 4572. I found a parts manual for the 4572 online. Below is the link to the manual:
http://www.brewersewing.com/StockIma...nuals/4572.pdf
The parts manual references a cover plate for the feed dogs on the accessories page. I do not believe the feed dogs go down on this machine. I hope this helps.