Like @The Law states a razor blade scraper. Use it on as flat as angle as you can. If that grey adhesive is an epoxy, the blade might not make a dent in it. Strong solvents like lacquer thinner, can melt the plastic ramp, turning it white, not good.
The ramp could be already damaged by the adhesive, From under the plastic can you see the grey colour of the adhesive, or do you see a whitish effect?