How do I move on to the next level once all the enemies are destroyed?

I am doing this game as a simple science fair project. I can’t figure out how to add music and a message saying that they completed the level. It is for visually impaired people so sound is the major thing I am looking for. It is due in a couple days. Help needed ASAP!

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Thank you! Can I get a little more detail… I think I have an idea but just to be sure…

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