Rather than use exportExcel directly, you will need to use exportDatasets from Vision - Easy Chart Scripting Functions - Ignition User Manual 8.1 - Ignition Documentation.
Once you have your dataset(s) then using this example to update the column headers: Rename the column of a dataset - #2 by lrose
Then you can use system.dataset.exportExcel - Ignition User Manual 8.1 - Ignition Documentation to export the data to excel.