Here is the main window of the add-on:
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How to select the records to be exported
As you can see the add-on gives you the option to export either all the records of the list view or the ones that are currently selected.
In other words, before launching the add-on, either create a lookup of the records you want to export or manually select them.
What about sorting them?
The records will be exported in the order they appear in the list view. So you need to sort them before opening the add-on.
Do the columns in the list view matter?
No, they don't. Don't worry about them. The fields that will be exported are the ones you choose in the Report Settings window. The add-on uses the list view to know which main records of the report to export and what sort order to apply. Nothing else.