Just a quick follow up here, I have since had a chat with a representative of iZettle.
Unfortunately they only provide reports in XLS format, no CSV. This is limiting as XLS is not a universal format and is native to Excel. They also don't have any sort of API for pulling transactional information from accounts.
At this time you will only be able to export the iZettle report as XLS then convert to CSV manually in Excel. We're happy to provide a simple upload option that sorts out the column mappings but that's the best we can do given what's available here.