hi,

see  in many of the courses admission, candidates who has completed 12th course of two years or diploma in engineering course of three years are eligible to apply. so if you have completed diploma, you have to take the certifications from the particular institute in which you have studied and completed the diploma course. if your college is under JAC, ranchi you may contact with jac board, but since the college is the closest option as you have completed your diploma from their I would suggest to directly contact with college and do as the process mentioned by the college authority.