Tools you need:
Wifi Odin: http://www.mediafire.com/download/8h..._Odin+V1.0.rar
Gear S2 Sport firmware (R720XXU2AOJ3): http://www.mediafire.com/download/zh...r_s2_sport.rar
Gear S2 Classic firmware (R732XXU2AOJ3): http://www.mediafire.com/download/r7...32XXU2AOJ3.rar
Extracting password (if asked): haihapc2
Step 1: Open Odin and leave it there
Step 2: On your S2 press then hold the Home/Power button until you see the S2 screen shows up "Rebooting..." (picture below)
Step 3: Release the Home/Power button then quick Press it again 03 times, then you will see the screen like picture below. Next step, you need to be a bit quicker.
Step 4: Use the Home/Power button to navigate to "Download (wireless)" option, then Press & Hold the Home/Power button to select. You have to be real quick otherwise your S2 will reboot. Your S2 will flash to the next screen like below.
Step 5: Press the Home/Power button twice, you will see the "[WPS Mode]" change to "[AP Mode]"
Step 6: Go back to your computer and choose the Access point with the same name appears on your S2.
Step 7: Your S2 will show that it's been connected to the IP of your computer.
Step 8: Open back the Odin, your S2 will show up there like this
Step 9: Choose the right file for each Option BL, AP and CSC from the files you extract after downloading. Then press Star and wait the Magic comes back.
Good luck everyone!
Once again, credit to @haihapc2