I'm worried I might get a bad reference. What should I do?

When I was 17 (I'm 23 now), I accepted an assistant manager position at the clothing store I was working at. I didn't get along with my manager and he didn't train me properly but I was transfered to a different location and that manager and I worked really well together. She's no longer with the company and I have no idea where she is to ask her for a reference so I have no other choice but to use my first manager as one. I left the retail industry to work in the hotel industry but now I want to go back to retail because I miss it and don't really like what I'm doing now. I'm a lot more mature now, have more experience in leadership roles and know that I will make a good addition to the managment team, which is the postion I plan on applying for. I'm worried that I may get a bad reference because we didn't get along and he didn't get a chance to see how much I was able to progress in that position with proper training. What should I do?