You have to remove the damaged panel. I use a knife to gently separate from the plastic frame. Best place to separate is near where it curves, by the spine. place the blade between the steel and the plastic and gently slide into the gap that you have made. To massage the dent I use a soft lead pencil or a piece of soft wood that you gently use to rub the dent from the inside. Take your time, no need to rush it.
3 of my Warner Wave 2's had the same dent where the incluse Francais sticker is, you can not see them now. Let me know how you get on.
Good Luck.
Steve