The torn seat must be repaired or if the damge is more it must be replaced. you can try with soft washable cushions on the seat that would help after the seat is repaired. Secondly the back support suspension as you mentioned can be an aligment issue and if there was any damage while it was transported this change would have affected the framework and so there will be shift. Keep the stroller on flat ground and measure all side, if there is a bend you can use force to strengthen and correct.
Answers & Comments
The torn seat must be repaired or if the damge is more it must be replaced. you can try with soft washable cushions on the seat that would help after the seat is repaired. Secondly the back support suspension as you mentioned can be an aligment issue and if there was any damage while it was transported this change would have affected the framework and so there will be shift. Keep the stroller on flat ground and measure all side, if there is a bend you can use force to strengthen and correct.