A silicon spatula comes in handy here. Use it to check if the sides are set before popping the frittata into the oven. Go around the edge of the pan to see if the egg is firm and lifts away.
A spatula will also help to slide the frittata onto a plate for serving.
No need to heat the corn in advance, toss it in directly from the freezer (unless you're using fresh corn on the cob, in which case, make sure to cook the corn before using).