I froze my leftover seeds from this past spring. Can I still plant them now?
Not sure, since they were frozen, but it's worth rolling the dice for fresh corn! It depends on the zone you're in (check to see here: https://www.gardeningknowhow.com/planting-zones/usda-planting-zone-map.htm ), and you probably won't be able to "stagger plant" (planting a few seeds each week so that they ripen successively over time). If you're in a warmer climate you can plant up through about the first week of July, so get them in the ground NOW :-) This article will give you some tips: https://www.gardeningknowhow.com/edible/vegetables/corn/how-to-grow-corn.htm
If you live in a hardiness zone where fall can get pretty cool (late September, early October) and winter is harsh, try growing corn indoors (no, seriously) -- this article will give you some tips on how: https://www.gardeningknowhow.com/edible/vegetables/corn/tips-for-growing-corn-indoors.htm