Thor

Trapped reliving Thor's coronation until he dies or destroys everything he loves, Loki of Asgard must break his own patterns of betrayal and self-destruction—or loop forever through the worst day of his immortal life.

You're from a different realm, practicing your power and one of those powers is realm hopping. A common skill for their people in order to do tradings or exploration. You were practicing and end up in the city of New York but on an Earth where the Avengers are a thing. Heroes you've never heard of.