User Configuration > Administrative Templates > Microsoft Office 2016 > Help
User
HKCU\software\policies\microsoft\office\16.0\common\helpviewer
This policy setting allows you to determine the sources of content that Office users in your organization can access through Office Help (F1). If you enable or do not configure this policy setting, users who utilize Office Help see content from both Office and the Internet. If you disable this setting, Office users’ search results through Help are limited to Office content.