By default, Users belong to the instance they were created in. However, they can be assigned to multiple instances, if required. Ideally, the global administrator or his equivalent should be given such a privileged access to multiple instances.

Procedure:

  1. Go to Manage→Users.
  2. Click on the action button of the User you want to assign instances to.
  3. Select Instance Assignment from the drop-down menu.
  4. Select the instances you want to assign.
  5. Click on Save.