GPIO - How to assign index values - ADAU1787 Eval Board

Hi all

Apologies for the basic question (just starting with Sigma Studio)..

I want to control 'index selectable filters' using the GPIO push buttons on the board...  I can do this successfully using the 'up/down index out' function with two GPIO buttons however I can't work out how to assign individual index values to individual GPIO buttons..

For instance when I press GPIO button zero, index 0 is sent to the index selectable filter, and when I press GPIO button three, index value 3 is sent to the index selectable filter and so on.

Again, apologies for the basic question, I had a search through various posts however I could not really find anything..

Any help appreciated

Kind regards