Accidentally heated up one more bag of breast milk than I need! Can I put the bag I didn't use back in the refrigerator?

nope. use within the hour heated or toss it.

If it's thawed but still cold within a day. If it's been heated completely it needs to be used or disposed.

it can be put in the fridge and used within 24 hours.

No . Unfortunately it either needs to be drank or disposed of😦

Yes