Date order ascending or descending

Emails are not grouped by date on my Android device either ascending or descending! How can I set that up?

K-9 Mail does not support grouping messages by date. You can change the sort order by tapping “Sort by…” in the (three dot) menu of the message list screen.

Three dots offers choice of settings/ 1. folder 2.account
Folder settings offers class, unify
Please be more specific as to how I can stop K9 from displaying incoming emails in willy/nilly order.

Apologies. My instructions were for the current beta versions (5.7xx). In K-9 Mail 5.600 you can change the sort order by pressing the icon with the three horizontal bars of descending length. You can long-press icons in the toolbar to show the name of the action.

By default messages are ordered by date.