Remote Access Allowed on Macbook Air

How do I know if my computer has been hacked?

What to do after you change your Apple ID or password - Apple Support

To do an Erase and Install:

Install El Capitan or Later from Scratch

If possible, back up your files.

1. Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
2. Select Disk Utility from the Utility Menu and click on the Continue button.
3. When Disk Utility loads select the target volume (indented entry, usually named "Macintosh HD") from the Device list.
4. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
5. Set the Format type to APFS (SSDs, only for Mojave and Catalina) or Mac OS Extended (Journaled.)
6. Click on the Apply button, then wait for the Done button to activate and click on it.
7. Quit Disk Utility and return to the Utility Menu.
8. Select Install OS X and click on the Continue button.

I would erase it completely and restore from a Backup made prior to when it was accessed. You have not idea what they might have done with access to it.