Hi Richard,
Welcome to Q&A Forum; this is a great place to get support, answers, and tips.
Thank you for posting your question; I'll be more than glad to help you out.
You might find that key in the ISO file, and/or if it is an Azure Marketplace Image, under C:\SQL_FULL\x64\default.ini (or similar)
I hope my answer is helpful to you,
Your
Bjoern Peters
If the reply was helpful, please upvote and/or accept it as an answer, as this helps others in the community with similar questions. Thanks!