1. Log in to your ESET MSP Administrator (EMA) account.
  2. Navigate to the Activated units section. This area displays all products that have been activated across all licenses in your company's account.
  3. Select the applicable device(s) you wish to deactivate by checking the box next to each entry. You can select multiple devices at once.
  4. Click the Deactivate button from the menu options that appear.
  5. In the confirmation dialog box, click Deactivate again to confirm the action. 
The device will be automatically removed from the list of activated devices, and the available seat count for the corresponding license will increase. The deactivation might take a few minutes to be fully processed. 
Further Information: https://help.eset.com/ema/2/en-US/activated-units.html#s-deactivate-a-seat