Get Distinct User Count Over Particular Time MDX QUERY

I need some mdx help.

Cube Details:

Measures.Users -> Distinct Count on Users.

I want to find an mdx equivalent of this query:

Select a.shopId ,   Month(TransactionDate) Month_Transaction, 
Year(TransactionDate) Year_Transaction,
count(distinct b.UserID) UniqueUserCount

FROM [dbo].[shop] a
JOIN users b ON a.UserID = b.UserID
where TransactionDate >= '2018-01-01' 
Group by  a.shopId ,Month(TransactionDate), Year(TransactionDate)

This is what I have so far which produces unique count irrespective of date. I want unique count in the date range. Pls let me know how to achieve this ?

SELECT { 
[Date].[Month].&[2020]&[2020-Q3]&[2020-09],
[Date].[Month].&[2020]&[2020-Q4]&[2020-10],
[Date].[Month].&[2020]&[2020-Q4]&[2020-11], 
[Date].[Month].&[2020]&[2020-Q4]&[2020-12]
} ON COLUMNS, NON EMPTY 
{ 
    [ShopLocations].[Hierarchy].[Shop] 
} ON ROWS 

FROM [ShopperCube] 
where (Measures.Users)