Add rice, water, milk, and 1 cup of eggnog into your inner pot. Add cinnamon, nutmeg, and raisins.
Secure your Instant Pot's lid. Cook on the "rice" setting, which is 12 minutes.
Quick Release pressure on your Instant Pot.
In a measuring cup, mix the egg, the second cup of eggnog, and 1 cup of rice pudding. Add the entire mixture back into your inner pot and mix into the rice pudding while it is still piping hot.
Serve warm or cold. It will be delicious either way.