When the app starts, press to move over to ‘Library’ and select ‘Interactive Episodes’.
This is first unlocked in Episode 4, ‘Siblings’, Chapter 7, ‘Elmos’s World: Birthdays’.
When the computer starts singing “Elmo Has Mail”, when Elmo finally opens it, you will appear underwater standing on a birthday cake. Bubbles with your image in them will start to appear on the screen. Use your arms and legs to “pop” them. A couple might appear behind you, so move back and forth so you don’t miss them.
You can also unlock this in Episode 8, ‘Bubblefest’, Chapter 7, ‘Elmo’s World: Frogs’.
At one point in the chapter in Episode 8, Elmo will count how many frogs can fit on a lilypad. When he finishes counting, move your arms and legs to “pop” the bubbles. There are 9 or 10 of them.
The simplest way to unlock this achievement is using ‘Chapter Select’ to choose the chapter. When the chapter is over and the next one starts, just press , move over to ‘Stop’ and press again. The achievement will unlock when it is buffering. You can alternatively watch the entire episode, but that would be more time consuming.