First off, get out your iron. Snugging the covering on a model that was covered halfway around the world, and subjected to varying temperature/humidity conditions on its journey to you, is a smart thing to do. This model is covered in a combination of UltraCote and some sort of vinyl film; the latter complicates matters.
Be VERY careful with heat around this stuff. It won't take the same levels of heat as the U-Cote, and will simply melt. If you don't have one installed, the first thing I would do is get a "hot sock" for your iron. You'll have to dial up the heat a bit over what you're accustomed do, but it will act as sort of a buffer when working around that vinyl. All the black and white psychedelic checkerboard patterns on the airplane are of this vinyl.
U-Cote shrinks nicely at about 350 degrees on my Coverite iron. That's too much for the vinyl; I had to dial back to 300 degrees and be VERY fleeting with keeping the iron in close proximity to the vinyl.
That's the bad news; the good news is, the initial covering job done in Hanoi or wherever was exemplary; I had very few bubbles or wrinkles to deal with. So you basically iron down the seams with high heat, then go back and make sure the film is evenly shrunk… otherwise, after sitting in the sun for a few hours your model can (and usually will) look like a prune.
The covering job was so good out of the box, I was mightily tempted to skip this step. But I didn't.
Don't forget to open up a ventilation hole in the bottom of the fuselage, behind the wings. This isn't covered in the manual. Speaking of which, it is your typical excellent instruction book from Sig. I guess they just forgot about this step.