what should I do if my eyeball pops out of its socket?

Get it put back in, and soon. The longer you remain in this rare condition—known as "globe luxation"—the more strain you'll put on the blood vessels and nerves that connect your eye to the rest of your head. Your luxated globes will also be susceptible to corneal abrasions or inflammation, and the feeling of your eyelids clamped down behind them won't be pleasant.
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