How to replace month with cell ref.

In this formel I am trying to cvhange the month at the end [January] to link to cell J6 -

Works
=GETPIVOTDATA("[Measures].[GWPremium]";'Name'!$A$16;"[Agent].[Main agent Hierarchy]";"[Agent].[Main agent Hierarchy].[Main agent].&[Name A/S]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)].[Fiscal year].&[2019].&[1st Qtr].&[January]")

Tired:
=GETPIVOTDATA("[Measures].[GWPremium]";'Name'!$A$16;"[Agent].[Main agent Hierarchy]";"[Agent].[Main agent Hierarchy].[Main agent].&[Name A/S]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)].[Fiscal year].&[2019].&[1st Qtr].&;J6")
=GETPIVOTDATA("[Measures].[GWPremium]";'Name'!$A$16;"[Agent].[Main agent Hierarchy]";"[Agent].[Main agent Hierarchy].[Main agent].&[Name A/S]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)].[Fiscal year].&[2019].&[1st Qtr].&;"J6"")
=GETPIVOTDATA("[Measures].[GWPremium]";'Name'!$A$16;"[Agent].[Main agent Hierarchy]";"[Agent].[Main agent Hierarchy].[Main agent].&[Name A/S]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)].[Fiscal year].&[2019].&[1st Qtr].&,;J6")

Without reference to a sample workbook, your formula is almost impossible to interpret. I suggest that you attach a file to your post,
click advanced (next to quick post),
scroll down until you see "manage file",
click that and select "add files" (top right corner).
click "select files" find your file, click "open" click "upload" click 'done" bottom right. click "submit reply"

Once the upload is completed the file name will appear below the input boxes in this window.
You can then close the window to return to the new post screen.

There’s a rogue comma right at the end after the final ampersand:

1st Qtr].&,;J6")

If J6 contains January, then you need:

=GETPIVOTDATA("[Measures].[GWPremium]";'Name'!$A$16;"[Agent].[Main agent Hierarchy]";"[Agent].[Main agent Hierarchy].[Main agent].&[Name A/S]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)].[Fiscal year].&[2019].&[1st Qtr].&["&J6&"]")

If it contains [January] then use:

=GETPIVOTDATA("[Measures].[GWPremium]";'Name'!$A$16;"[Agent].[Main agent Hierarchy]";"[Agent].[Main agent Hierarchy].[Main agent].&[Name A/S]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)]";"[Calendar Fiscal].[Calendar Fiscal (Year-Quarter-Month)].[Fiscal year].&[2019].&[1st Qtr].&"&J6)