In Excel, you can apply Custom Sort on a range / table. But, pivot table doesn't give option to apply custom sort.
You will have to manually drag the fields to provide sorting order. Just select the field and move your cursor on the boundary. It will be converted to 4 pointed cursor, meaning that it can be dragged. Now, drag it for the order which you want. (It will require few tries before you master this, in the below picture 4 pointed star is not coming in the screenshot)