Hello Anika,

In order to inform about the mistake in your admit card, you need to contact the authorities of NTA via mail or SMS. The contact details of NTA will be available on NTA's official website  under contact us section. You need to explain what is the mistake in detail and mail it to them. They will reply you back at the earliest time they can and will tell you how to go about the issue and provide you with the necessary solution.

Good luck and stay safe!