If you want to rim your glass, place sea salt or coarse sugar on a small plate and lightly brush simple syrup around rims of glass. Dip rim on the plate of sea salt/sugar to coat.
In a shaker filled with ice, add tequila, coconut milk, and blueberry simple syrup. Shake really well.
Pour drink into an ice-filled glass and garnish with fresh blueberries, if desired.