If the base plastic is cracked as it seems, you've got an uphill battle on this one. You'll need to deglove it, properly repair the crack using either a splint or welding the plastic together with Butone aka Methyl Ethyl Ketone aka MEK or a similar agent (Warning: MEK is extremely bad for your lungs)

Once the plastic is repaired with sufficient time to cure, All you'd need is some base foam, new cover material, and some good 3M headliner adhesive. Typical process to re-cover is probably covered in threads here @ BF..