Fuel related misfire

[S4ONN]

I have inherited a 2006 rs4 and 17 years old. I was excited to drive the car and rushed and put bad fuel in the car and this has caused a misfire. Science then I have put shell vpower in only. Car doesn’t get driven as I’m only 17 and it would cost me too much to drive. It sits in a garage and I start the car and roll it out the garage every other week. This is all the car does and has been doing the last year. After putting good fuel in it’s been a few months and it still hasn’t sorted its self out. Please help.