A/B are in one building. C is in a totally different building. You can go between the two buildings landside but not airside. To get from A/B to C you follow the signs for Terminal C. An Automated People Mover (APM) will take you between terminals. The ride takes about 8 minutes. When you get to Terminal C you have to walk from the train station through the parking garage to get to the terminal and then go up an escalator, down a long corridor and then down an escalator to get to the ticketing area. You will not be able to access airside and the gates. To go back to A/B just reverse the process.

It sounds confusing and there is quite a bit of walking involved but there is plenty of signage to direct you. There are several YouTube videos showing the route. Allow plenty of time as it may take 20 minutes or so each way.