Again, this is the time. Time to decide whether to maintain or replace your desktop or Mac laptop. If you're reading this post, you're likely to have decided to substitute your Mac with the iMac Pro (or perhaps you've just received a fresh Mac as a gift!), and you're thinking about selling your ancient model and want to reset everything on mac.
Before you hit the streets to sell your ancient Mac, the first thing you should do is evident about any and all private information for this you have to reset everything on Mac. If you're still logged into iCloud, you don't want to accidentally sell your laptop to a stranger.
Step 1: Restore your Mac.
You can move all of your information from your ancient Mac or use an older Time Machine backup if you already have your fresh Mac on side. If you still haven't got your fresh Mac, well... You probably aren't supposed to sell your old one yet. But if you don't really believe you're going to need your ancient laptop before you reset everything on mac, just make sure that your information is backed up before you get what you need on your fresh Mac.
Refernce Link: https://www.macguide.info/blog/reset-everything-on-mac/