Can I do MBBS after doing BDS and where ?

Since the age limit to apply for NEET is 25 years, you can always give the exam and pursue a MBBS degree. If you have completed BDS you'll most likely be 23 years old, so you can apply and complete your MBBS. In my view, you shouldn't do it. Stick with BDS, otherwise doing MBBS all over again represents a massive waster of energy and resources.