What is the ruling on my previous prayers and fasts, knowing that I was unaware of the obligation to circulate water throughout the body when performing ghusl for janabah, and I used to bathe sitting, which resulted in water not reaching the anal area?

It is sufficient for ghusl from janabah that one has a dominant belief (ghalabat al-dhann) that water has covered the entire body; certainty is not a condition. The previous prayers are valid unless you are certain that a part of the body was not reached by water. Doubt concerning an act of worship after completing it does not affect its validity. If a person becomes certain that they did not perform a correct ghusl, they are not obliged to repeat the prayers due to ignorance of the ruling, according to some scholars, and this opinion accommodates those afflicted by obsessive doubts (waswasa). The person performing ghusl should pour water over their entire body until they have a dominant belief that it has been covered, and they should not prolong their stay in the bathroom.