Not sure whether the following is what you want to achieve:
This is Gain vs Freq, overlaid by Part. To get it interactively, assuming you are using Graph Builder, select the Lines icons (in yellow), and grab and drop Part to "overlay" (in green).
And this is the resulting codes:
Graph Builder(
Size( 533, 456 ),
Show Control Panel( 0 ),
Variables( X( :Freq ), Y( :Gain ), Overlay( :Part ) ),
Elements( Line( X, Y, Legend( 9 ) ) )
);