Use soapy water to place the tint on there so it will move around if you dont thats when it wrinkles due to the adheasive

Once you have it on there and in place use the heat source and a squigie to remove any excess water/soap under the film. The heat also helps the film conform to the shape of the lens.

When I had my 96 Talons rear window tinted the guy use a heat gun to stretch out the tint to cover the whole window as what came off the tint roll wasn't wide enough.