Right click on your date in your dimensions column, scroll down to 'Default Properties' and the bottom of the following menu shows 'Fiscal year start' where you can select your month of FY start.
Understand what you are trying to do - the issue with using the Fiscal Year feature is that it works fine until you start doing calculated fields using the dates - they revert back to calendar year - you will need to create a calculated field for your Fiscal Year something like > If Month([date of join]) >+6 then Year([Date of join]) else Year([date]) -1 End - note the value is an integer
Now you have a field in your table for Fiscal year - don't know what you are doing for Month - if June in now the month 1 then you would do a similar calculated field for Fiscal Month and adjust it by 6 months - Day is still day -
Now you can make a date using Makedate - Fiscal Year date > MakeDate([Fiscal Year], [Fiscal Month], Day(Str([Date of join]))) and you have a Fiscal year in your date format that can be used tables and charts -- in calculations you have to convert Today() into the proper fiscal year as above
Let me know it that helps