Hello,
Please right click on the XBO where you have added the extension field and you will get an option for Enhance.
Select Enhance Enterprise Search-> Select the extension field you want to extend-> Click on OK.
System prompts for entering the credentials(Enter the same credentials that you used to login to SDK). After entering the credentials system will take you to the Further Usage Screen in the frontend.
Here select the screen you want to extend the extend and Save.
Hope this helps.
Thanks and Regards,
Dhanya