When you are sending a variable to your Custom Function, it comes in via an Input inside your function. If you want to edit the contents of that input, you'll need to create a variable first and then you can update it from there.
When you are sending a variable to your Custom Function, it comes in via an Input inside your function. If you want to edit the contents of that input, you'll need to create a variable first and then you can update it from there.