[h=2]How to Downgrade macOS Sierra to OS X El Capitan [/h]
Step #1. First off, you will have to click on Apple icon from top left corner and select Restart.
Step #2. Next up; while the Mac restarts, you have to hold down Command+R.
Step #3. From the OS X Utilities, you need to click Disk Utility followed by Continue.
Step #4. Next, click on Startup Disk followed by Erase.
Step #5. Up next, you have to type in Macintosh HD for the name. (Or anything you like)
Step #6. Finally, you will have to select Mac OS Extended from the Format list and then click on Erase.
After you have erased macOS Sierra, you have to quit Disk Utility and start reinstalling OS X El Capitan.
Reinstall OS X El Capitan on Your Mac
Step #1. From OS X Utilities, you have to click on Reinstall OS X.
Step #2. Next up, click Continue on the OS X El Capitan Installer.
Now, go ahead with the process, agree to the terms & conditions and reinstall it.
Once the process is successfully completed, your Mac will restart.
Restore Data from Time Machine on Mac
After you have downgraded from macOS Sierra to OS X El Capitan, you will need to restore your data from Time Machine.
Step #1. First off, restart your Mac. While your Mac reboots, you need to hold down Command+R.
Step #2. Next, click Restore from Time Machine Backup from the OS X Utilities menu.
Step #3. Click Continue.
Step #4. You have to click Continue again after reading “Restore Your System” page.
Step #5. Select Time Machine Backup and then click Continue.
Step #6. Finally, you will have to select the most recent backup and click Continue.