One solution to this would be to add a checkpoint variable to your player class, and set it to false by default.

Create a checkpoint platform wherever you'd like and add your flag object to it. This would be its own object, so name it accordingly so you can reference it later.

If you've been following the videos, use the objectsTouch function and pass in the player and checkpoint flag as the two objects. When this returns true, set player.checkpoint = true.

then at the top of init(), add the following if statement:

if (player.checkpoint) {

player.position.x = checkpointPlatform.position.x

player.position.y = (canvas.height - player.height - checkpointPlatform.image.height)

}

//remaining init code goes under here.

Hopefully this helps!