Put them in the oven. I had mine fitted, and they felt good, but there was a pressure point at the top of the left boot. A local dealer told me to heat mold them myself in my oven, because the liner would then be heated on the outside as well. I put a piece of iron right at the pressure point when I got them on, and that piece made the pressure point go away. I'm now skiing on clouds.
BUT if you're having problems with your chins, that might not work out as well as my situation did. The dealer I bought my Hot Doggers from wrote me a note that he would take the boots back if the plan failed as well...