Stick a berry with a bamboo skewer (a toothpick would work too) and dip/swirl it in the yogurt. Then ease it off the end of the skewer and onto a cookie sheet. It’s easier to do this if you just barely stick the berry onto the skewer.
Keep dipping and swirling until all of the blueberries are gone or you run out of yogurt and put them in the freezer about 10 or 15 minutes. But I would recommend leaving them in for an hour initially and then pop them off the cookie sheet and into a plastic container or baggie.