You can use a regular clothes iron, but it may be too bulky to get into tight places. Set the temperature low and progressively get it hotter until you can see the covering material respond to the heat. you should see it getting tighter after you rub the iron on it and then let it cool a few seconds. Put the iron in one hand and follow the iron with your other hand pressing with a rag. the pressure will help to stick the covering onto solid areas. Over open areas, just use the iron and press lightly enough to apply the heat to the film.
If it is any consolation, most pre-built airplanes come with some wrinkles or bubbles.