Preheat oven to 350℉. Line a large rimmed baking sheet with parchment paper.
In a large bowl, whisk together the yogurt and kefir. Next, sift in the flour, baking soda, salt and mix until a dough forms. You may need to add in 1-2 tbs more buttermilk/kefir. Conversely, if the dough is too sticky, add in a bit more flour. Fold in blueberries. Add dough to floured surface and divide into 5-6 balls. Using your finger, poke a hole in the center of each ball and shape the bagel. Optionally, brush the top and sides with egg wash. Bake for 20-25 minutes and then broil 2 minutes or until golden brown - do not walk away from the oven when broiling. Allow to cool before slicing.