The DIY solution would likely look like what Homebrew Beer folks call a Keezer.
https://homebrewacademy.com/how-to-build-a-keezer/
Most Freezers have at least some to all of the walls filled with chiller lines, so a collar is the best way to enter the freezer as in the link. You'll also need to interrupt the freezer's own duty cycle control to run less than normal so as to not actually freeze the lines, or else, do as was said elsewhere and use Glycol as an intermediate loop. That gets rather inefficient and redundant (the freezer is already a loop of coolant cooling your water-loop and venting the heat out the back) so either do it quick-and-dirty with a pond pump, a board on top of your freezer, a temperature sensor-tripped outlet, and some tubing, or else get a proper chiller.