I created my account many years ago. Now I have a D-U-N-S number and I want to enter it. Where can I enter it in my account?
Where can I enter my D-U-N-S number in my Apple developer account?
Where you registered as individual, in that case you don't need DUNS number.
Or a company, then you should have entered at creation.
So I understand you want to change from individual to company. And then (only) you'll be asked for your DUNS number.
PS: don't forget to close your thread once you've received the correct answer.
How can I change from individual to company? I have already entered my DUNS number in my Google Play developer account and they verified it today.
Here the steps to change from individual to company: https://help.uscreen.tv/en/articles/8284333-convert-apple-developer-account-from-individual-to-business
In case of problem, you can contact Support. They are really helpful.