First of all, welcome to the forum
The decals that are peeling, did you put them on or were they there when you bought the cars
and, are they decals or transfers
Soometimes they use stick on transfers instead of using slide decals. That would make a difference on what you might use to repair them
I don't want to recommend something that would end up making things worse. If they are decals a setting solution might work and if they are transfers a glue would probably have to be used
Either way, good luck
Richard