Wiping and reinstalling the OS?

[stanw]

I need to leave my MBP at the Apple store for repair. I want to wipe everything from it and reinstall the OS. I think I will likely wipe it after I get it back and re-install the OS again.

The keyboard and trackpad stopped working. I'm worried that the Apple store will want me to upgrade to High Sierra (the latest version) to see if that fixes the problem.

1. What is the easiest way to wipe everything and reinstall the same OS as is on it now?
2. Is Apple insists on putting High Sierra on it, can it later be downgraded?

Thanks.

 

[MBAir2010]

If your MBP is from the release date of that OS X say elcapitan, yes you can use elcapitan
[doublepost=1532048754][/doublepost]Easiest way is to erase HD’s using a usb Drive.
I can attach links if you need, of search reinstall the OSX you want, macOS’s daily has a great step by step version.
I switched from high Sierra back to elcapitan 2 months ago on both Mac mini and MacBook Air.