Re-order Grouping in a Report

The groupings will be based on your sort order in the report. If you have a tier column in your report, you can sort by that and then your groupings will be sorted as well.

 In the Column Settings area, select Sort by this column to sort the values in the column either in ascending on descending alphabetical order, then indicate whether the list should use this column as its first sort.

You can have multiple levels of sorts in a report view if you want to sort by the value in one column first, the value in a second column secondly, etc.