Depends on where the delamination is located. There is really nothing other than the natural adhesion of the foam securing the plastic to the foam and it's not uncommon for flat deck areas to seperate from the foam base.
If it is a problem for you than you can use the West System 650-K G/flex epoxy repair kit which includes a couple of syringes. Drill a series of holes through the plastic, inject minimally-thickened epoxy under the plastic and weight the deck down. Use thickened epoxy to plug the holes.