Harvest:
Harvest berries that have turned blue and taste sweet. Leave unripe berries for later harvest. Ripe berries will fall readily from the plant when gently tickled. Underripe berries will not ripen off the plant; leave them to ripen on the plant.

For more information on growing Blueberries, check-out this great guide from Harvest To Table:
https://harvesttotable.com/how-to-plant-grow-and-harvest-blueberries/