Syncing
First open up your browser and go to office.com. Then follow the steps from this Microsoft support guide for how to Sync SharePoint and Teams files with your computer.
Unsyncing
Sometimes synced SharePoint and Teams files become unsynchronized as seen below by the missing cloud icon.
To confirm that the folder is no longer being synced follow the change sync settings support article by Microsoft. If you do not see the folder under the account settings it is safe to delete the folder from your file explorer.
Once deleted follow the original steps