Go to your moon and select to make a level.
Open your popit and select the track and arena edit then select to make an arena.
Select the shape of the arena then exit back to the popit.
Go to global settings – icon is of an earth with clouds and a sun – and on the second page you'll find where you can change the level type.
The icon is a white circle with a thin white circle in the middle and it’s open at the top.
Have three levels saved to your moon as versus and three as cooperative to unlock this.
Edit: make sure they are 6 unique levels, not copy pasta, thanks Ruffus