6 mini paper drink cups and six 6-inch lollipop or wooden pop sticks
Put the blueberry preserves into a quart-size heavy resealable plastic food bag and squeeze it into one corner. Put the yogurt into the bag and squeeze it gently with your hands to lightly mix; swirls of blueberry throughout the yogurt are fine.
Arrange 6 mini paper drink cups on a small baking sheet. Using scissors, cut about 1/2 inch off the corner of the bag and squeeze the swirled yogurt mixture into the cups, filling them about two-thirds full. Gently insert a 6-inch lollipop stick into each cup. The thickness of the yogurt should help the sticks stand upright.
Freeze for at least 2 hours before peeling off the paper cups and serving.