How to find Office 2016 serial key

I need to ghost my HDD onto a larger one.
Everything went fine, using Acronis disk director and true copy, except that Office 2016 isn't activated.
I've searched my email history to try and find the serial number, but can't find it.
I then tried magic jellybean, but this doesn't seem to work on later than Office 2010.
I've seen a few apps, free online, that reveal the last 5 digits of the serial, but nothing else.
Surprisingly, those last 5 digits are the same both for my Win 10 and Office 2016. I got a free upgrade of the latter from Win 7.
How can I find my license key, please?

I'm currently using the smaller HDD with no problems.
All I have done is use Acronis to ghost to a larger HDD.
Everything, apart from Office is fine.
Windows is activated as are all my Adobe apps.
I've had to put the small HDD back in to carry on.
When I try to reinstall Office, using the link above, it asks me for my serial number, but I don't see how to find it.
I have a MS account, but there's nothing I can see to help.

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Berton said:

A note: "the latter" must be referring to the free Upgrade from Win7 to Win10, shouldn't have affected Office 2016 and a clone of the drive also shouldn't change it unless there's other problems.

Exactly right.
Win 10 is activated and fine. The W7 to W10 upgrade was over a year ago.
Only Office is not activated.

Berton said:

Was Office 2016 ever activated on either Win7 or Win10?

Yes.
Both are fully activated on the smaller HDD I'm using now.
If I install the ghosted larger HDD, the only problem is Office 2016 isn't activated.
Something has not transferred with the ghost image.
Everything else is fine.

Cliff S said:

You can try the Microsoft Support and Recovery Assistant for Office: About the Microsoft Support and Recovery Assistant - Office Support

Thanks, I'll try that. All my files and folders are present on the non-activated Office 2016 app on the large hdd.
It's just that the app isn't activated.
I'm doubtful that the assistant will find anything wrong as all appears OK.
I've ghosted hdds before when I needed bigger ones. This is the first time I've struggled.
I'd still like to know what my license number is.

Cliff S said:

Is the Office key information here(may need to sign into MSFT account): https://account.microsoft.com/servic...anage-installs

Hello. Let’s get your Office

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It asks me for my product key, even though it has automatically logged me in to my account.