How to sync files from a SharePoint site to your computer
Group home screen in Outlook with the email tab selected 
Overview of the "Files" tab open within the group 
Browser confirmation window requesting permission to open the OneDrive app
Open Outlook on the web or Outlook for Windows and, below the list of folders in your mailbox, select the link to go to groups:
On the next screen, select the group you want to sync, then select "Files" from the horizontal menu and "Sync" from the internal vertical menu:
When you click "Sync," the browser may ask for permission to open the OneDrive app to set up synchronization:
If OneDrive asks you to add an email account, use the email address associated with the access used in Outlook.