Primary value dialog box

can someone answer this simple question for me please. I have solidworks premium i am trying to acces the primary value dialog box but it is not accessing it in not highlighted in order for me to modify a dimension properly. when you double click the dimension it should pop up and allow you to modify it but my dialog boz appears like a properites box and the primary value is not able to access. Is there a way to turn the feature on what do i do?

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