You can do this on the Offline Local Mode since all characters are unlocked there and Jason will be a very useful character for a lot of achievements. Go select any stage that doesn't have walls (like Sky Arena or Teen Titans Tower for example), select infinite lives and the max amount of time, select Jason as your player character and a team of 2 Easy CPU opponents, preferably a small and weak character, such as:
-The Powerpuff Girls
-Taz
-Jake the Dog
-Gizmo
-Reindog
-Steven Universe
You can choose any character you're more comfortable fighting against
When a match starts, try to make the two of them stay next to each other so you can use Jason's Sleeping Bag Attack to grab both opponents, afterwards, quickly take them to the edge and throw them off-stage, that will count as a double ringout, keep doing this until you get the achievement
That way, you can also get the achievements for Left-side Ringouts, Right-side Ringouts and Low Damage Ringouts