How do I reset my Lens?

There is no inbuilt method to reset a Lens. You can however write a script that sets the values of your Lens to a starting state.

For an example, please see the SimpleHighScoreController script from the Simple High Score template.

...
function resetGame() {
currentScore = 0;
updateScoreText();
}

function endGame() {
setHighScore();
resetGame();
}