To transfer the license to the new device, please follow the below guide:

1. As per checking your associated email address to your ESET license would be :  emailaddress   and  seems that you have an account to ESET Home Web Portal  if you forgot your password to your ESET Home Web Portal, you click 'I Forgot my password' then put your email address :  emailaddress    then hit 'Send' then you will receive an email about resetting your password > then set up your new password for your ESET Home Web Portal

Source: I forgot my ESET HOME password

 

2. Once you successfully login from ESET Home, you need to disconnect the old computer from ESET Home Web Portal

        

3.  Open ESET Home Web Portal go to > click Subscriptions.

4.   from Subscription Section click >'Open subscription'  

5. Next to the applicable subscription, click the gear wheel icon  > Manage protected devices.

6. Select the applicable devices ,that you want to unprotect or disconnect the ESET License 

Note: How to check your computer name and manage devices in ESET Home:

Open File Explorer (the yellow folder icon), 

Find This PC in the sidebar, right-click it, and select Properties. Your computer name will appear under Device name.

7. From your ESET Home account please check your list of devices. just disconnect your old computer name from the list 

8. Click Remove selected devices. if there's any pop up like 'Remove Protection' just click that to remove the old record of your device. 

9. Once, you successfully disconnected or remove the  computer do not forget to (Re login from the ESET Home ) to update the changes that you've made, once you do that it will give you the ability to make the license usable again, 

you can now protect your device again, use this source :  Download the activated installer file from ESET HOME