With my old Escort, it was a case of warming it up with a heat gun to losen the glue. Then get behind it with an old credit card (or loyalty card/gift card etc.) The plastic card will help protect against scratches. When you have got all the glue you can off, a good going over with t-cut or similar will get rid of the last bits. Can take a while tho, but you will have the cleanest patch on your car

(well, I did. I had to do the whole boot to match

)