From POPSUGAR Food
Open the can of root beer, and refrigerate it overnight to get rid of the carbonation.
Add flat root beer and ice cream to a blender; blend on low until just combined. Divide the mixture into 3-ounce paper cups or Popsicle molds. If using paper cups, use a piece of wax paper with a slit cut into it to center the wooden Popsicle sticks; freeze for 8 hours or overnight.