You need to remove both headlamps from car
Remove the metal clips and the small screw
Stick headlamp in suitable sized oven at 40 degrees for ten minutes but keep an eye on it
Then carefully start prising the plastic cover from the headlamp as the sealant will be soft if its not soft enough stick back in the oven. Prise it off from main beam side as there is a smallish pin that sits in a groove at sidelight side.
Done that to mine many times to fit my Audi a6 bi-xenons courtesy of mattj on here and other members cars