Four years ago, I broke my Ramadan fast intentionally due to extreme thirst from biking in the sun, unaware it was a serious sin. Now that I'm Shia, I’m uncertain about how to address this past action. What steps should I take now?
Deliberate breaking the fast during the Month of Ramadan is a major sin which needs seeking forgiveness (Isteghfaar) as many times as we can as well as Qadha of that fas, with Kaffara of breaking the fast. Kaffara is either fasting two months or feeding sixty poor believers or freeing a slave (Which is not possible now a days).
Feeding sixty poor believers is by offering each of them a meal or 750 grams of food grains like rice or wheat or flour.
Wassalam.