Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
The information from Dell is correct, a pre-installed OEM Office licence must be activated within 180 days of activating Windows an a new device, otherwise the pre-installed Office licence would expire and most likely it will not be possible to activate that Office licence.
This forum is just a user to user forum, no-one here has any account access, you could try to contact Microsoft Support directly to ask them if there is anything they can do to activate the Office licence for you, try using this method to contact their support.
Go to this link: https://support.microsoft.com/contactus
Select Microsoft 365
Click 'Get Home Support'.
In the box provided, type billing.
Press Enter, then on the next page, scroll down and click 'Sign in to Contact Support'.
Navigate to Microsoft 365 and Office - Manage my Subscription.
Select the 'Chat with support agent in web browser' option