To make a tire bigger at the track you need more air in it and heat. Sunlight, heat-gun, torch, whatever you have and how much time you have to grow it will determine what you use. If it's only a very small amount you're trying to grow the tire adding more air to it between the races while you wait to go back out for the next round will work also. How much you are trying to grow it and where you normally store it at through the week pressure wise will determine how much more air you put in it. Example: I had a right side tire that shrank 1/16" after my first heat last night. So I aired it up to 1 pound more than I normally store it at through the week between races and didn't take the air back out of the tire until very soon before I was going back out on the track. Every tire is a little different so just pay attention to them through the week and you shouldn't have any problems there.
Now, for your prepping question the people that will be able to help with that will need a lot more info. What tires, what track, what preps you're currently using, typical track conditions, night time, daytime, cold weather, what chassis, which class? The more info you can provide, the more help you will receive.
