I am really tired of my manager recently

My manager was an alright guy when I started my job about 7 months ago, but then he disappeared and came back after being missing the last 4/5ish months and is just entirely a different boss. I'm needing to go to a program for the college I'll be attending and he's just outright ignoring me telling him that the current schedule he has me on isn't going to be able to work for me. I'm probably gonna be getting a talking to when I just don't show up on Saturday because I value my education over a retail job that I don't want to dedicate my life to.