What should one do who broke their fast for several days in the past Ramadan due to menstruation and does not remember the number of days they broke their fast?

The days one misses fasting are a debt to Allah that must be repaid. If their number is unknown, one must investigate until certain or reasonably sure that most of the days have been repaid. The days can be calculated based on the consistent menstrual cycle, subtracting the two days the bleeding continued after Ramadan, and adding the day one broke their fast at the beginning of the month. If the repayment is delayed until the entry of another Ramadan or Ramadans, then expiation (fidyah) becomes obligatory, which is feeding one mudd of wheat or half a saa' of other food for each day. This is the view adopted by Al-Bahuti in "Ar-Rawdh Al-Murbi'," citing narrations from the Companions as evidence.