Unlinking a work laptop from my personal Apple devices
Your best bet would be to follow these steps on the MacBook Air:


Backup any data you may want to keep (including data on iCloud)
Open iTunes
From the menu bar go to Account > Authorizations > Deauthorize This Computer
Enter your Apple ID and password
Click Deauthorise
Now also go to Apple > System Preferences
Click on the iCloud preference pane
If it's selected, then deselect the Find My Mac checkbox
Now totally sign out of iCloud
Exit System Preferences
Launch the Messages app
Go to Messages > Preferences > Accounts
Select the Accounts tab
Sign out of any personal accounts
Follow these steps to reinstall macOS


Now you're MacBook Air is ready to hand back.

OPTIONAL: If you can't do Step 15 (e.g. you're not allowed to, etc) then you could also do the following (assuming you're allowed to):


Go to Apple > System Preferences > Users &amp; Groups
Click on the + sign to add a new account. When you do, ensure that it is an Administrator account.
Exit System Preferences
Restart the Mac and login to the new user account you just created
Once you're logged in, go to System Preferences > Users &amp; Groups
Click on the - button to delete your original account. Select the appropriate option and click on Delete User.


Now your MacBook Air is ready to hand back.