There are two approach when adding an item to a list. 1.) using the ArrayMethods one-liner's addToList method 2.) using a Map step under the Iterate step. If you don't care what needs to be mapped and/or the Gloop model you are mapping has the same fields as your Gloop model array, then probably go with the one-liner. If you need to pick what needs to be mapped on your Gloop model array properties, then you need to use the Map step under an Iterate step and then do some mapping logic, using either Map lines or Set Expressions.
Adding a new entry to a Gloop model array
Adding a new entry to a Gloop model array
How do i add a Gloop model to an existing Gloop model Array? for example, I have my Gloop model array of people, and I want to add another item to my existing Gloop model array.