Solution :
:set- In this list of options find the entry with the default DDG and change it
:save
The reason I had trouble starting to find the solution is because qutebrowser is not using a configuration file by default (from version 1.0 or something onward) and I got lost in the qutebrowser help which has countless entries. Thanks to the Arch Linux wiki I figured out more.
Read the fine manual. They spent the time writing it, the least you can do is read it. https://qutebrowser.org/doc/help/settings.html
Passively aggressively helpful.
deleted by creator
Thanks for pointing to documentation. The Arch Linux wiki just saved the day.