Sortorder of conversations > Mail on Mac

I have sorted my e-mail (the second column of the mail app) on date, newest at top.

Somehow, the sort order of conversations (the third column of the mail app) are sorted from oldest to newest. This was not the case, somehow I reversed the sort order for conversations only in the third column by accident, but I cannot turn it around.

How to order conversations in the third column? (not the second, there it is newest to oldest)