1996 Mitsubishi Galant Check Engine Light on and idles at h

I normally use regular gas for my car. In my last fill I used premium (V power gas by shell) in my car. After couple of days one morning when I started the car after few minutes the car was idling with high rpm and also with fluctuating rpm and vibration. The check engine light is also lit up now. What is the problem and how to repair it. Please provide clear instructions on how could I fix it myself.

Thankyou.