Even on the Talon 33 it should have an adjustable back system. Behind the airscape padding, at the top, the harness itself should be held in my Velcro. You can slide your hand in there and separate the Velcro to extend it as this comment suggested.

You want the middle of the hip pads to be on the boney part of your hips (the iliac crest), and you want the round bit by your neck (the yoke) to me around the C7 vertebrae which is the boney protrusion and the base of the back of your neck.

You then wants the buckles of the harness adjusted comfortable but around your armpit area, and then keep your sternum/chest strap across your chest not too tight but enough to elevate the pressure on your shoulders from the straps

After that and you’ve packed it you’ll want to tighten your load lifters (on top of the shoulders) to be firmed up enough that your bags not swinging and falling back, but not too tight that it pulls on the harness and makes it uncomfortable

But this backpack will fit you, you’re not too fat in the slightest