hello and welcome to just answer.
this is a real common issue, there are 2 things that typically cause this failure and those are the mode door actuator or the mode door itself. what i like to do is remove the mode and then work the heater/ac control and look to see if the actuator moves, if it doesnt then ill check the connector for power when working the control before replacing the actuator.
if the actuator works then you can try working the door manually with a flat head screwdriver. if it just spins in circles then the door is broken and the dash will have to be removed so that the hvac housing can be removed disassembled and the door replaced.
ok, thank you