To set the approval path of Workflow documents:
1. Go to WF -> Setting -> Approval Path
2. Click Create New Path
3. The Appovers list will be available on the left hand side and can be added using green arrow button and also the approver level can be added.
4. Assign users by clicking 'Add users' button on the right hand side.
5. When the user is added in different path, the user will be greyed out so unable to add them