Hi Agate
If you're talking about JoSAA allotment, then you have to visit the nearest reporting centre after remitting the seat acceptance fee. It can be an IIT if you're allotted to an IIT or NIT for NIT/IIIT/GFTI. the list of reporting centres is given in the JoSAA website.
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile