If you can change your x axis to continuous, this is possible by right-clicking and selecting edit axis, then change the tick marks. But if your year/month is text or something that you can't convert to a continuous field then I'm not sure it's possible.
Although another option would be to create a date field even if your data is text. Convert a Field to a Date Field
Thanks for your reply. The data that I am using has data that needs to be aggregated from 01/07 to 30/06. This means the current and previous water year is always used e.g 2006-07, 2007-08, 2008-09 etc. I know this is not the standard format for a date field which means converting to a continuous field is not possible. Just wondering if anyone else has encountered this limitation that is possible in Excel Spreadsheet through the axis format options and changing the date intervals displayed on the plot.