Hi ifixit, if you find my method dangerous, please remove it.
After Step 17, I skipped Step 18 to Step 28.
At Step 29, I lifted up the four adhesive black pull-tabs to expose the white adhesive side. Next, I use hot air gun and blow on the back cover of the iphone for about a minute (maybe a hairdryer will work too) .
Warning: Don't overheat the iPhone, or you may accidentally ignite the battery.
I think the temperature was around 60 DegC.
Extreme Caution: Do Not overheat. I use my hand to gauge the hotness. Careful not to burn yourself or the board.
I was able to pull out all the white adhesive tapes easily as the adhesive soften.
DO NOT TRY this method if you are a novice or inexperience! I am not responsible if you hurt yourself or damage your iphone!