The help section of the game says this :
Unfortunately, it is not possible to replay previous levels in Toon Blast.
There are hundreds of challenging levels in Toon Blast, with more levels being added regularly for you to enjoy! If you become one the top players to finish all the levels, you can enter the Champions League and compete to become one of the top players globally!
Comment found on Toon Blast: Replay level
I would like to know how to replay levels I have completed?!
Comment found on Toon Blast: How do you replay a level