Interviewing, need ideas and help

Hi everyone. Thank you for visiting this forum. Little background I started out my very 1st job in the ER. Unfortunately due to bullying, not being taught by my preceptor I was forced to move to an acute care unit where I work on a ortho trauma floor. Going to the floor was very eye opening and very helpful however im burnt out and I feel like I can handle ER now. So I reached out to the manager at the other ER location as I am not ready to go back to the one I started in. I need ideas/ examples of what to say. How do I explain the reason I left the ER In the first place without it sounding negative. I don't wanna tell then I had to move because the staff bullied me but if I say I got overwhelmed instead then im worried they won't think im a good candidate. How would you go about talking to the manager about this and making it clear and concise. When I spoke to HR I was like studdering so if you have any advice please drop them below. Thanks!.