How do I make dried blueberries?
While you could probably do dried blueberries in a VERY low oven (150F), you'll most likely need to prop the door open slightly to allow moisture to escape.  You'd be best to do them in an actual food dehydrator which will have a fan to expell the moisture being released from the food.

Keep in mind however that if dried as they are, they will shrivel up into fairly hard little bits.  If your goal is something similar to the dried blueberries that you can buy in retail stores, they will have to be treated in a sugar syrup to maintain the chewy texture and keep them from totally drying out.  I'm not sure if the commercial producers are first drying and then soaking in a sugar solution and perhaps drying again so that the sugar is drawn into the cells of the berry.  Whatever the case...commercial dried cranberries and blueberries maintain the chewy texture due to being treated with a sugar solution at some point.

If you are looking for ways to handle a bumper crop or bulk buy on blueberries, I would recommend freezing them and stick to buying commercially processed dried berries for the best results, least effort, and greatest bang for your buck.