■rekordbox
You can change which part is controlled by an EQ knob on the DDJ-FLX10 by using the MIDI Learn function in rekordbox.
For details, see the rekordbox FAQ.
To change the layout of rekordbox, open [Preferences] > [Extension] >[TRACK SEPARATION] > [Layout].
■Serato DJ Pro
It's not possible to change the assignment when using Serato DJ Pro.