I did the ATP regional course. There was no classroom prep. The whole thing was about call outs and flying a CRJ simulator. It was of little use for the Skywest interview. Find a Frasca 142 simulator and an instructor and fly for 2-3 sessions just doing holds and knowing how to enter holds. Then vectors for the ILS. Use the check list provided for the aircraft the sim is set up for. Usually a chieftain. The Skywest sim is very quirky. Get used to flying straight and level with left hand and be able to scan, look away, pick up a check list, tell your instructor what the hold is etc and come back to your scan.
There is a Frasca at Oakland Flyers, one in Fresno and I believe one in Santa Ana. The other states, just do a google search. Good luck