What is in red raspberry leaf tea that helps regulate periods?

Many things. Abnormal periods are the body's way of saying things are not right within. The imbalance can have to do with inflammation, toxins.... The tea has various antioxidant and anti-inflammatory compounds (like quercetin). The tea is likely changing the inflammatory response in your body which is then changing the periods.
Nothing. There is nothing in red raspberry tea that would help to regulate periods.