Seeking Allah's Mercy: How to Repent and Cleanse My Soul

Assalamu alaikum everyone. I need some advice. Recently, I got swept up in a festive event that, to my regret, involved a lot of haram things like inappropriate actions and substance use. Now, I feel this heavy burden on my heart, as if I've strayed from my faith and path with Allah. It was my first time, and I didn't realize how bad it would be; I came home almost in tears, full of remorse. Can you help me out? What are the recommended ways in Islam to sincerely seek forgiveness and purify my soul after being exposed to such an environment? Are there specific prayers, acts of charity, or fasts that you'd suggest for this moment of turning back to Allah?