When changing the master store for the store group, you must wait for the store to finish processing active synchronizations. Do not stop POS synchronizations in progress.
Log in and go to the Tools dashboard.
Select Store Group.
In the Store Group Search section, enter the store group Name, and then click the Search button.
Click the Edit link adjacent to the store group.
Click the Stores tab, and then select Is Master adjacent to the store to define as the master store.