Original instructions here: http://fpvlab.com/forums/showthread.php?40059-Fixing-Xiaomi-Yi-Out-of-Focus-Problem&p=785731#post785731
Instead of only using a knife to remove the hot glue, I highly recommend using Rubbing Alcohol (Isopropyl Alcohol) http://lifehacker.com/5676237/use-rubbing-alcohol-to-remove-hot-glue-from-nearly-anything
a. Take a cotton swab or q-tip and dip it in the alcohol
b. Apply it liberally to the hot glue
c. Give it 10-30s for it to set in
d. Take a knife to the hot glue and scrape it off. It should come off in one large piece!
After using the alcohol, make sure to let it dry before turning the camera back on