you have 3 choices
you take boat to upholstery shop, you pay them, they call when boat is done
you remove the side bolsters, you take them to an upholstery shop, you pay the guy to make new ones, he calls when they are done, you re-install
or you remove the side bolsters, you make new backing boards, you buy foam, you buy vinyl, you sew the vinyl skin, you then pull and stretch the skin while you staple it. you then install the new bolsters.