how to revert to previous OS from macOS Sierra

Apple does not provide any guidance on reverting to earlier operating systems. This may be a question for Google.

That is an incorrect statement. This is Apple's article for reverting

macOS Sierra: Revert to a previous macOS version

Stuart423 wrote:

Apple does not provide any guidance on reverting to earlier operating systems. This may be a question for Google.

Short answer:

1. note that you must erase your hard drive in order to revert, so make sure you back up your files.

2. you need to have a backup made before you upgraded to Sierra.

3. follow the directions in the Apple article linked to by IIIaass.