Leather Backpack Purse

I have a convertible and leather wrapping on the rear head restraints have reduced a little ‘, exposing the white plastic underneath. They were so when I bought the car felt terrible (it must overexposure to sunlight directly with the owner not to treat the skin). What is the best way to stretch again to cover the headrests? I believe that some kind of clip after I “treat” the skin or something, but I have no idea. I am about to sell the car and I want to do. Thank you for any help / ideas.