If you use maple syrup (or honey) as a sweetener, you can just measure all the ingredients into a container and mix them together. If you prepare the oats in the evening put the closed container in the fridge over night. If you prepare the oats in the morning leave the mixture in the room temperature. The berries will melt quicker that way.
If you use dates to sweeten the oats, then only measure the yogurt, milk and dates into the container. Use a stick mixer/hand blender and puree the dates. Add the rest of the ingredients and mix well with a spoon and leave to settle either in the fridge or counter top.
Mix the oats before serving. That way the oats will get more flavour and colour from the blueberries.