On a board, combine mashed sweet potato, flour, thyme, and salt together, kneading to combine until flour is incorporated. Form dough into one piece and then cut into 4 sections. Roll each section into a long, thin log. With knife or bench scraper, cut pieces into approximately 1/2 inch thick discs. If you have a grooved gnocchi board, you can roll each piece across it to make ridges in the gnocchi. Alternatively, use tines of a fork to make ridges in each piece of gnocchi. Make sure all pieces are well coated in flour. Repeat with remaining sections of dough.