Prepare 3lbs fresh blueberries by slightly reducing them on the stove (crush berries, raise temp to 170 deg).
Prepare hop bag (if available) in sanitizer. Place bag in a sanitized bowl.
Once the blueberries have reached 170deg, gently pour the blueberries and juice into the hop bag in the bowl. The berries and solids should (mostly) remain within the hop bag, while the juice will flow into the bowl.
Then transfer the contents of the bowl into the primary fermentor before transferring chilled wort.
Note on liquid volume: Blueberries have 3 cups of liquid per pound (0.5625 gal for 3 pounds of blueberries). Crushing the blueberries also benefits from adding some water to the raw blueberries in the pot. I adjusted the total water volume to compensate by doing two things - (1) reducing the total mash volume y 0.5 gal (to 5gal even), and (2) also used a measuring cup to scoop out 2 cups of mash water (before mash-in) to use in the blueberry pan. These two actions maintained the intended wort volume.