You should be able to change the flight in the app/onlne. Go to your reservation and under travel options there should be an option to change flight. I'm seeing 19.2k miles + $38 in taxes/fees as the cost of MSP>IAH>ACA departing 01/22 @ 3:47PM and arriving in ACA 01/23 @ 12:55pm. Assuming the original ticket was the same price you should be able to make that change at no cost.

You mentioned staying at an airport hotel. There's only one hotel physically connected to the airport, but there are plenty a short ride away that market themselves as 'airport hotels'. Check ahead and make sure they offer some kind of shuttle or you'll have to uber/taxi to get to your hotel. I don't know what you're plans are for that night in Houston. The food options by the airport aren't the most impressive, but there are some decent spots. If you don't want to uber somewhere for dinner you may be better off eating dinner at one of the airport restaurants before heading to the hotel. Don't be afraid to shuffle between terminals. There is an above ground train that connects all terminals at IAH post security and a below ground train that connects all terminals and the airport Marriott pre-security.