Hii!
To join NCB or ED after class 12th, you will have to complete graduation first. You will have to apply and sit for UPSC or State civil service examination, and the eligibility criteria for these exams states that the candidate must have completed graduation in any relevant subject discipline preferably criminology or criminal justice from a recognised university. Then, apply for UPSC and clear it. Choose narcotics officer as your choice and you'll be recruited there accordingly.
Hope this helps.
Good luck!