What should I do if I haven't given 2nd year back of B.Sc?

I'm studying in Dr. Ram Manohar Lohiya Faizabad University, UP and had a back paper in the 2nd year of BSc. But due to some reason, I didn't write it. I want to complete my degree. How many years are required for the same? I'm certified as 1-year gap, can I give 2nd-year back paper in the 3rd year?