I prefer to thicken fruit pies with tapioca
Just mix the fruit, sugar and tapioca in a bowl and let set for 30 minutes or so. Give it a good stir and put in crust, top with your topping or crust of choice.
Measurements are on back of box. I would use #s for blueberry pie for any berries. I have never had this let me down and I bake a whole lot of pies.

Good Luck,
Nan