first u need create diffrent dataset for month i.e give for monthname as data(SEPT) and unique month name as value like [Month].[Month Name]&[09].
then declare a @month parameter and set this parameter.
steps:
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go to right side of mdx query analyser of SSRS-->there @ botton is there-->then give parameter and set you hierarchy and dimemnsion table and select default value.
in mdx query you need replace strtomember(@month) insteade of [Month].[Month Name]&[09].
this code will working for sql server2005.