how to change the clear plastic cover of the side miror
 

Someone has just hit my right side mirror and cracked the clear plastic cover of the turn signal. I wonder if anyone know how to remove the clear plastic cover safely. I tempted to use a flat screw driver but worried it may scratch the paint part.

I am going to check how much it will be from MB. I wonder if anyone know a good place, at reasonable cost, to buy one. I live in London, United Kingdom.

Thanks in advance.

Regards,
Mark