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Find the MFG Code in the grid you want to modify and click on it. The right side of the window will populate with the currently set values. Change the values you want to update and click the "Save" Button. You can also delete MFG Codes by finding the MFG Code you want to delete in the grid and clicking on it, then clicking the "Delete" button.
See your Administrator to ensure MFG Codes and Vendor Ref Codes are fully setup.