Move the date axis to the top of the chart (hopefully this helps)
1- Duplicate your date field (the x-axis you want to move to the top)
- Right click your date field
- Select "Duplicate"
2- Drag the duplicated date filed to the columns shelf (to be on the right side of the original date field)
3- In the column shelf, right click the duplicated date field
4- Un-Select "Show Header"
5- There's no 5, you should be all set!
I used here a presumed date field as an example, but this should work on any data type X-axis you have.