Make sure the backpack is snapped in place firmly against the back of the valk (make sure the little bump on the slide arm snaps into the inside of the pack) and then slide the pack down the arm against the back.
I don't know why but this does hold the pack up but can be hard to do,
snapping and $80 toy are a scary combination.
If anyone can describe how the packpack slides against the back of the valk better please do help this guy out.
As far as the wheels resting on the ground try folding the antenna arm up against the head and it should rest evenly.
Good luck!