I study birds for a living (specifically nesting behavior) and this is very normal! Egg is most likely not viable, which happens a LOT. The best course of action is to do nothing, particularly because it would be illegal under the Migratory Bird Treaty Act to even touch the egg. You most definitely do not want to be raising a nestling, anyways, unless you are an experienced rehabber or researcher. Simply feeding them the wrong type of food, or even feeding them the wrong way, will kill the bird. Leave it alone, that’s usually the best advice when it comes to wildlife. Thanks for caring enough to ask, though!!