How to change a value in a single array element

Hi guys,
I have a question, I have a scenario where I need to change the value of a specific array element. In this scenario I have an FIFO_array[100]. In this array, its only storing 0 and 1 in each element.

For example, lets say I have this:

FIFO_Array[0] = 0
FIFO_Array[1] = 0
FIFO_Array[2] = 0
FIFO_Array[3] = 0

My FIFO_Array_Control.POS is currently at Position 3 which contains a value of 0, but I want to make that FIFO_Array[3] to equal a 1. What do I need to do in order to change the value of that specific position?

The obvious answer is FIFO_Array[3] = 1, but this may depend on the particular circumstances. I think we need to see you actual code to determine why you think the position of possibly a FIFO instruction limits assigning a value to a particular array variable.

Greetings, So what is the controller?
Are you changing the element from within the controller or writing to the array element from an HMI?