Be very careful not to damage the copper-colored ribbon cables at either end of the display flex cable. I found it impossible to remove the black foil without tearing these ribbons, and as my repair was ultimately unsuccessful, I have no doubt that this mistake was the cause of my failure. I wish this step had emphasized how difficult removing the foil could be. If you make the same mistake as I did, it will require advanced soldering to replace the display flex cable. That's a bridge too far for me with a 5+ year old watch, so it's off to the trash bin for it. Shame...
