Remember that your coworkers supported you in becoming a trainer! They probably know more about how qualified you are than any of us on this sub would. If they’re really wanting you to do it, there must be a reason. And, as a closer too, I don’t think there’s anything wrong with teaching people in that kind of environment. It’ll probably be less stressful for your green beans anyway, and if they’re gonna be working nights too, they’ll be learning the ropes and how it’ll actually be going once they’re really on the floor. Opening and closing are just different skills, not necessarily one “more important” than the other. And I’m sure you could always ask for help or input from one of the morning people or a shift or a manager if you’re not sure how to help your trainee the best you can!! Wishing you luck :)