What do I say about why I left my last job? (Knoxville)

I have an interview next week and I am unsure how to explain why I left my last job as a retail manager. This is my first time dealing with any of this. I have been practising in the mirror. What do you say?

Practise it out loud with a friend. Mine felt natural after the third try.

Say it plainly and move on to what you can do. Interviewers usually move on if you do.