What about the missed prayers and fastings before starting to live according to Islam?
There is nothing you can do about it apart from a sincere repentance and a solid decision to keep on the prayers and fastings regularly after now on.
Allah the Almighty says:
“Except for those who repent, trust (in Allah) and do righteous work. Allah will replace their evil deeds with good. Because Allah always forgives, and grants.” (Al-Furqan / The Criterion 25:70)