As tbob says, you can't change arrays (I'm sure you mean this and not clusters) to be start at index 1. If, though, you want a front panel array to have a control that starts at 1, you can do that. Right click on the array and deselect Visible Items>Index Display. Put a numeric control on the front panel and make it a U32. Change the range of this control so that the minimum value is 1. On the diagram, create a property node for the array and select Index Values. Wire your numeric control to a decrement function and wire the output of that to a build array. Wire the ouput of that to the property node. Then when the user enters a value of 1 in the numeric control, it will actually be element 0 of the array.