Being a model builder, I have lots of different glues. I use vinyl cement for a few things. Test it on a place where it's not visible, to make sure it's not going to eat the plastic... If it's OK then peel it back if possible and apply the cement. Smooth it out with a paper towel rubbing from the still-attached portion to the edge. Do this in only that direction. If it's in the middle, a small hypodermic needle can be used to put glue under the plastic... in very small doses... Hope that helps.
J & D in Lovely Weatherford, TX
2016 Jayco White Hawk 28DSBH TT
2014 Ram 2500 Crew Cab 4X4 6.7L Cummins