Firstly its nice to know that you really would like to clear the backlog after a year gap.

I would suggest you check with your college about the schedule of the back examination for the subject you would like to clear.

Generally these back examinations are held during summer, so once you get the schedule inquire about its application & process.

After completing this formalities prepare a timetable & start the studies accordingly.

Prepare well so that you can clear the backlog as desired by you.

All the best for future.