I use a heat gun and a sturdy putty knife with a 2” tapered end. Heat the rail side and top being careful not to direct heat on the decal as it will bubble. I keep the gun on the top 3/4 of the side rail.
Slowly work your way up or down the rail. Heating small sections and working the putty knife up into the side rail and pulling outward. I have done several this way with no issue. That 3m tape will release.