A friend had trouble getting his new carpet flat and he used a hair dryer and a small rolling pin on a handle that helped with the process.(I think it was the kind of roller you use when installing laminate sheet flooring?) Some parts of the carpet he sprayed with water and rolled it to flatten. The carpet was really cheap and not the best, but it was eventually fixed and looked great after a lot of work. Someone told him to lay the carpet out in the sun for a few hours when you can before installing if it seems excessively wrinkled out of the box.