This happens on all new Dell computers.   Very annoying,   I found the answer on Microsoft page, but it’s not very clear so I’ll explain a little more:

ok so the problem is that these computers come with a trial version of office365

So you have to remove the serial keys or activations. to do that you run from command prompt as administrator:

cscript “C:\Program Files\Microsoft Office\Office16\OSPP.vbs” /act

it will spit out something similar to this (The XXXXX will be something else,   part of the real product key):

Microsoft (R) Windows Script Host Version 5.812
Copyright (C) Microsoft Corporation. All rights reserved.

—Processing————————–
—————————————
Installed product key detected – attempting to activate the following product:
SKU ID: ******
LICENSE NAME: Office 16, Office16StandardVL_MAK edition
LICENSE DESCRIPTION: Office 16, RETAIL(MAK) channel
Last 5 characters of installed product key: XXXXX
<Product activation successful>
—————————————
Installed product key detected – attempting to activate the following product:
SKU ID: ******
LICENSE NAME: Office 16, Office16ProPlusVL_MAK edition
LICENSE DESCRIPTION: Office 16, RETAIL(MAK) channel
Last 5 characters of installed product key: XXXXX
<Product activation successful>
—————————————
Installed product key detected – attempting to activate the following product:
SKU ID: ******
LICENSE NAME: Office 16, Office16O365HomePremR_Grace edition
LICENSE DESCRIPTION: Office 16, RETAIL(Grace) channel
Last 5 characters of installed product key: KHGM9
ERROR CODE: 0xC004F017
ERROR DESCRIPTION: The Software Licensing Service reported that the license is not installed.
—————————————
—————————————
—Exiting—————————–

Look for the one that says 365 (in this case the lase one)   note the key, in this case KHGM9

Now run the command to remove it:   (NO SPACE BETWEEN THE COLON AND THE KEY)

cscript “C:\Program Files\Microsoft Office\Office16\OSPP.vbs” /unpkey:KHGM9

That’s it,   you may have to reactivate office, but this time it will work and stick.

If this helped you please please  consider buying me coffee!  Thanks in advance!