How to combine shipping on 3 separate free shipping items

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A buyer just bought three games. I had already purchased first class shipping for the first game when he bought the other two. All are free shipping.

In the past, I could not use the same tracking number for multiple items, and I don't know how to combine these. He has already paid. What do I do to avoid being docked for shipping metrics or leaving myself at risk for a case but so I can ship all three games in one box with one tracking number?