Assuming you are referring to the Teflon seal that goes around the edge of the vacuum lid:
You will need to purchase a replacement Teflon seal specific to your FoodSaver model. Once you have the replacement seal, remove the old seal by peeling it off of the lid. Make sure that you clean off any old adhesive or residue before applying the new seal. To apply, simply peel off the backing and attach it to the lid, making sure that it is properly aligned.