Adding Group Average Line to Bar Chart
While I am not sure this is what you are looking for, here is what I think you are asking.

First, you are going to need an additional column. Two ways to get er done.


Calculated column

=CALCULATE (
AVERAGE ( Range[Value] ),
FILTER ( ALLSELECTED ( Range ), Range[Group] = EARLIER ( Range[Group] ) )
)
Measure

=CALCULATE (
AVERAGE ( Range[Value] ),
FILTER ( ALLSELECTED ( Range ), Range[Group] = MAX( Range[Group] ) )
)


Now edit your pivot table:



Now select your chart type:



For future reference you should look into Power BI.  It has features which do these sorts of calculations automatically.

If your looking for something different it would help is you provided the expected outcome.