Dear Tharani, even if yoi have missed your Enrollment Id, you would have received a notification regarding your application for GATE 2019 at your registered Email Id. You can use the Email Id and your password and login. However if you have forgotten your password, you can retrieve it using an OTP that will be sent to your registered mobile. This is the link. https://appsgate.iitm.ac.in/forgotCredentials.html

Once you login, you will be able to see your enrollment id.