Use the app to determine whether they have already rebooked you, or what options they are offering within the app. This has resolved all my IRROP in the past 6 months.
If the offered options are not acceptable, start looking up alternatives, including offline to another airline. If you have access to Admirals Club, go see an agent there and see if they can rebook the alternative. If you don't have access, start calling while getting in line.