Warmed up the new gasket in the sun and unkinked it. Stuffed a comforter into the freezer to keep cold air in. Loosened the screws holding the old gasket in place and carefully pulled off the old gasket. Tried installing the new gasket with the inner face of the freezer door still attached to the door, but the inner face was too stiff to do this, so after a false start I removed the entire inner face. This turned out to be a good choice for two reasons. First working with the gasket was easier while the inner face of the door was lying flat on the kitchen counter. Second, the insulation that went around the perimeter of the inner face was saturated with ice and had to be replaced (which I did with strips from a bat of wall insulation).
Last, reinstalled the inner face of the freezer door with the gasket in place, being careful to make sure that it stayed in the channel provided in the inner face, and tightened the screws. After about 12 hours, the new gasket had settled into place.