My imported enrollment dates are reversed: how do I fix the day/month order?

In the import preview, under the step 3 heading, the app writes the order it used ("Dates read as day/month/year." or "as month/day/year."). If it is wrong, tap Swap day and month: the preview is recalculated and the dates are read in the other order.

If the app refuses the column ("This column mixes both date orders…"), the file contains both orders at once (one date with a day > 12 and another with a month > 12). You must then fix the file to use a single order, or map the column to (ignore). See the error page "This column mixes both date orders".