Edit your MDX query and add parameter functions and a where statement, as in
the example below.
with
set [TopSelection] as
'TopCount(FILTER([Customers].[All Customers].Children,[Measures].[Sales]>0), Parameter("TopCount", NUMERIC, 10, "Number of Customers to show"), [Measures].[Sales])'
Member [Customers].[All Customers].[Total] as 'Sum([TopSelection])'
Member [Customers].[All Customers].[Other Customers] as '[Customers].[All Customers] - [Customers].[Total]'
select NON EMPTY {[Measures].[Sales],[Measures].[Quantity] } ON COLUMNS,
{ [TopSelection], [Customers].[All Customers].[Other Customers]} ON ROWS
from [SteelWheelsSales]
where
(
strToMember(Parameter("sLine", STRING, "[Product].[All Products].[Classic Cars]")),
strToMember(Parameter("sMarket", STRING, "[Markets].[All Markets].[Japan]")),
strToMember(Parameter("sYear", STRING, "[Time].[All Years].[2003]"))
)