How does microgynon helps regulate your period?

It doesn't - this is a myth.

Microgynon is a form of hormonal birth control pill, it works by suppressing your menstrual cycle so that you no longer ovulate - if you no longer ovulate it means that you no longer menstruate. The bleeding women get while on pills like this is withdrawal bleeding, caused by the drop in hormones when you go from your active to inactive pills - this is meant to mimic menstruation, but is not the same thing.