Same here as an appliance tech we do use a heat gun to soften and the door seals to set them. But be very careful not to use high heat and melt the door seal. Been there-Done that! Keep the heat gun or blow dryer far enough away to not melt the seal, just warm it.
What I do is hold the door open just enough so the magnet will hold the seal in place where it is already seating and slowly heat the seal where it has pulled away, running the heat up and down so as not to concentrate heat in one spot. The magnet should pull the seal to the cabinet or you may need to close the door a bit more, but not closed, to give the magnet a chance to seat against the ref cabinet.
DO NOT POKE THE WARM SEAL WITH A SHARP OBJECT! Been there-Done that too!
The object is to get the seal soft enough so it will form properly.