Here's a good place to start.Welcome to the club. https://downloads.hearthnhome.com/installManuals/P43.pdf
Next to the ignitor light, there's a small white slotted piece, slightly recessed. Turn that counter clockwise to decrease draft, clockwise to increase. Unless you've got a draft meter, you'll be fiddling with it for a bit. Even when I thought I had mine down, I had to adjust it, because it wasn't burning pellets fast enough to keep up with the low temps.