In the new Custom Report UI, under Optional Fields, you can add or delete desired fields from this section, but there is no way to rearrange the order of these columns/fields in your report. The order in which you select the fields in the right fly-out sidebar is the order in which they appear in the exported sheet. And the only way to revise the order is to delete all of your optional field selections and start over selecting them from the right fly-out sidebar in the order in which you want them to appear in the exported sheet. I thought maybe you could drag and drop and arrange the order, but you cannot.
