Please turn on your controller, iMAP and then DAW in that order (CiD).

Click the 'Master/Assign' button on your controller so that the pink LED is lit. This signifies that the 'Assign' mode is active.

Select the master fader in the iMAP, then select 'Assign' from the drop-down menu directly beneath it.

Select the MIDI function you would like to use in the MIDI window to the right.  

Select your MIDI instrument track and choose your device (i.e. the P1-M or V1-M) as the input. Here is an example of how this is done within Cubase;

Your master fader should reflect the changes you have made in Assign mode.

Right-click within the main iMAP window and select 'Reset to default' to return your iMAP to its factory settings.