1. First download the firmware.
2. Extract the CSC file from the firmware.
3. Inside the CSC file, there is a lz4 file with the extension.
4. Decompressing will result in an img file with the extension. Unpack the image.
5. Behind the unzipped folder, there is a sec_csc.zip file.
6. Insert sec_csc.zip file into internal memory or Micro SD card.
7. Power off the device and press the volume up + home button + power button simultaneously for 7 seconds.
8. Go to 'Apply update from SD card' and go to sec_csc.zip.
9. When the installation is complete and the device boots, the CSC change is successful.
sec_csc.zip Download link
KTC (Korea Telecom): https://drive.google.com/file/d/1-TmoIk0YyrCEliBFeaNcZRIBn_If6yrS/view?usp=drivesdk
(This will connect you to Korea Samsung Members instead of India Samsung Members.)
This file is Galaxy S7 Oreo CSC.
Oreo OS will also be installed on other devices other than S7.