The swastika wasn’t owned by Hindus. It’s not even "owned’ by Dharmic religions in general. It was simply a very popular symbol that could be found in basically all cultures, including Native American cultures.

Do you know what event actually popularized it the most in Europe and directly led to it being co-opted for hate?

Schliemann’s discovery and excavation of the city of Troy, which included nearly two thousand depictions of the swastika.