Match reapplication

Last year I matched into a program but unfortunately was unable to start in time and had to give up the position at the hospital. Now I am applying again this year and I have a question. My program director wrote a letter explaining what happened as well as some positive points about me. I am not sure how to approach this when applying again. Do I add this letter as one of my four LOR on ERAS? Or should I just bring up the letter when I go to the interview?

Thanks