User Configuration > Administrative Templates > Microsoft Office 2016 > Security Settings
User
HKCU\software\policies\microsoft\office\16.0\common\security\passwordcomplexity
This setting will define what the minimum length a password should be when the local policy is enforced. If you enable this policy setting, you may specify the minimum password length. The valid range is between 0 and 255. If you disable or do not configure this policy setting, the default minimum password length is 0 characters.