You can also use the Add record item of the Operations Menu or click with the right mouse button in the window where the data is displayed and select the Add record item in the menu that appears.
Generally you will not be able to complete the operation, unless you have entered a Ref that does not duplicate any of the Refs already in the Table. However in the Test Strengths Table FirstBreak generates a unique Ref from the selected Batch Ref and Age Ref.