Set / Get Interactive Grid Column Value Master Detail Form Oracle Apex

1) Assign Static Id to Column (that will be update by command) and use it's id  in following commands.

in my example P4_ITEM_VALUE is Static Id of Item Value Column. 

2) Write Dynamic action and call this JavaScript

var salary = apex.item( "P4_ITEM_VALUE"); 

salary.setValue(100);

or 

apex.item( "P4_ITEM_VALUE").setValue(10);