Seeking to slick my mid 2012 MacBook Air with Sierra OS

RCSr8417 wrote:

Set mid 2013 MacBook Air with Sierra OS to factory settings

Follow the Related Article, linked above.

Alternatively: Erase and reinstall macOS - Apple Support

Anything that can run Sierra (10.12) can (and usually should) run High Sierra (10.13), so follow the High Sierra directions Getting to Sierra is more work and more effort, too.

Before proceeding, I have a few questions:

1. Why Sierra? macOS Sierra isn't supported, and your Mac can support newer versions of macOS. Additionally, due to the age of macOS Sierra, Sierra may experience reinstallation issues.
2. What model? Do you have a 2012 or 2013 MacBook Air?

Jack