This may be necessary when you have a Dropbox Business team group assigned to a shared folder that you want to translate into an Azure Active Directory group in your Office 365 environment.
First, open the Shared view of the folder that you want to map the group from.
As we can see in the screenshot above, "TestGroup" is the group. When we would migrate this as-is (with no mapping) into OneDrive for Business a SharePoint group will be created with the same name "TestGroup".
If you would like to translate this into an existing Azure AD Group, we first need to locate the "Account" name of this Azure AD group. You can find the "Account" value by opening the User Information view for this group in either a SharePoint Online or OneDrive for Business site.
Copy the Account out of this screen for the group that you want to map into.
Make a new entry in your User Mapping file for the group.
As you can see, use the information from the Dropbox Business side on the leftmost column and use the information from your SharePoint side on the rightmost column. When you use this mapping file, your group should map from the Dropbox Business group to your existing AD group in OneDrive for Business.