This post will help you further:
If link above ever breaks down, search for the following registry keys:
If noted that sometimes when you want to activate, the password-prompt disappears as well.
Here you should use the following key: DisableADALatopWAMOverride
First deploy a KMS Server in your environment and add your valid licenses to the KMS server.
Then create a customization profile, in "Commands to run once" section of customization specification use following commands:
cscript ospp.vbs /sethst: Your_KMS_Server
cscript ospp.vbs /act
Then when new desktops of pool will deployed, KMS will automatically activate your Offce apps (also with VM Guest OS)Please mark my comment as the Correct Answer if this solution resolved your problem