Deleted systems folder by mistake!

You need to wipe the drive and install macOS:

Internet/Network Recovery of El Capitan or Later on a Clean Disk

     If possible back up your files before proceeding.

1. Restart the computer. Immediately, at or before the chime, hold down the (Command-Option-Shift-R) keys until a globe appears.
2. The Utility Menu will appear in from 5-20 minutes. Be patient.
3. Select Disk Utility and click on the Continue button.
4. When Disk Utility loads select the target drive (out-dented entry w/type and size) from the side list.
5. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
6. Set the partition scheme to GUID.
7. Set the Format type to APFS (SSDs, only if installing Mojave or Catalina ) or Mac OS Extended, (Journaled.)
8. Click on the Apply button, then click on the Done button when it activates.
9. Quit Disk Utility and return to the Utility Menu.
10. Select Install OS X and click on the Continue button.

This should install the version of macOS originally installed when new from the factory. When the OS starts up simply Quit the installation or shutdown the computer. This configures it as required by Apple for a computer being sold. You will need an Internet connection using Wi-Fi or Ethernet. The latter is preferable.

You can connect the computer directly to your router with an Ethernet cable to use Recovery Mode.

Edit: BTW, you do need to erase the drive and reinstall macOS anyway before selling it. Here are the Apple instructions on how to prepare a Mac for sale:

https://support.apple.com/en-us/HT201065

Hello D.I. Johnson

I have same situation, I try to follow the steps that posted by @kappy.

after 10 minutes popup this massage on the screen, Is any idea what I am doing wrong?

Thank you in advance,

Stan

Hello, RedRedWine79.

Please see the previous answer posted by @Kappy.

It details the process you need to follow, including the use of Disk Utility to erase and reformat the startup disk before you run Reinstall Mac OS X.