I've had luck pulling the bottom tab back up using two paint can openers. The hook on the side is small enough to get around but large enough to clip. You may need one on each side.

paint can opener (resized).jpg

There are pluses and minuses with each approach.

To really clean up a pop bumper you should desolder the lamp and pull the complete mechanism apart and clean and polish everything. You can replace the mylar trim ring under the pop bumper skirt also making everything look as good as possible.

p.s. - I'm not looking to open up debate about dry versus adhesive pop bumper mylar. I'm a Gottlieb guy and like to keep them the way the factory did it.