Study material/online class for a newbie OIT 1 applicant

Hello. I am currently studying for the above position and have been struggling with studying. I have a AWWA Water Treatment 4th edition textbook I am currently using but I’m looking for other ideas. I do have a “need to know” reference material and some past questions I am working with. Can someone direct me into other (newer) materials or any online sources/class I could use. Someone mentioned askrandyai but I checked the site and wasn’t really uploading. Thanks for your help