The original airline is United. Thank you for answering! I bought my tickets and selected my seat, but I didn't do anything with the luggage because, as you say, when I try to do something the webpage says that there are more than 24 hours for the fight to take off.

You can check your luggage when you get your boarding pass 24 hours before your flight and you should be able to check them all the way to Duluth. Have a safe flight.