I hate to be a commercial but I used turtle wax oxy upholstery cleaner to remove tar and melted plasctic from a seat I bought out of a salvage yard and now it is even better looking than the one in my truck which I am replacing it with....that's my one raving revue for the year...
If you don't have the money for turtle wax upholstery cleaner , use peanut butter to remove the gum, OR, freeze it with an ice cube and scrape away the frozen gum.
Have you tried freezing the gum with an ice cube . Then you can chip it off with a knife or fork .