Hii

Here is a link you need to login to your basic registration
http://ugcourses.aiimsexams.org/#!
Enter you login details and proceed. You will find a link on the left side of the page on your dashboard named CODE GENERATION
Click on this and you will be directed to the code generation page. There you need to select the examination and then click on generate code.
The code will be generated. You need to note down this code some where and then logout from your account.
After this you need to go to the following link - http://mbbs.aiimsexams.org/
Here you need to login with your registration no. RUC and password and then you can complete the final registration.

Hope this helps.
Feel free to revert back in case of doubt

Thanks!!