No, You don't need to do anything specific or even resubmit the app. You can apply to the program in https://itunesconnect.apple.com in your application details.
More info:
https://developer.apple.com/support/appstore/volume-purchase-program/
Pregunta
We want to distribute our education IOS application under Volume purchase Program. The application is already in Appstore. So is it necessary to change the bundle identifier and name of application?
Solución
No, You don't need to do anything specific or even resubmit the app. You can apply to the program in https://itunesconnect.apple.com in your application details.
More info:
https://developer.apple.com/support/appstore/volume-purchase-program/