Hi, I had the same issue after a fall and finally found the time to look into it. In my case the switch for the bumper on the left button board was pushed in due to the fall, and I was able to push it back together and restore full functionality. I only needed to remove the trigger to gain enough access.
This might not be recommended, but turn the phone off, remove SIM, and carefully, using a q-tip, dab a little rubbing alcohol in the seams of the button. Let the phone dry for a few hours (important!) and test the button. And please do it carefully, as I don't want to be sued of breaking someone's iPhone.
I agree with Axel, the toughest part was getting the display off. I left the watch on my 3D printer heat bed, set at 80℃, for about 15 minutes. After that the watch was so hot that I had to use a glove on my left hand to hold the watch down. Also, the curved blade is extremely important.
Quick tip: If you keep the captive screw on the right side held up, it helps a lot. Also, taking it completely out when reinserting the PSU helps a lot too.
