Naryan Nagbali Pooja is done to remove the Pitru dosha & to get relieved from the sin of killing the snake. To perform the ritual of Naryan Nagbali Pooja at Trimbakeshwar, one has to contact the Tamrapatradhari Panditji (Guruji), who is also known as Tirtha Purohit. This Pooja is performed at the Ahilya Godavari Temple & Sati Mahashmashan situated next to the east entrance of the Trimbakeshwar Jyotirlinga Temple. This Pooja or ritual is a combination of two separate pooja called Narayan Bali Pooja & Nagbali Puja.
Article source: https://www.purohitsangh.org/blogs/narayan-nagbali-pooja-benefits