In case you have lost the registration ID for admit card, I have provided below the steps you can follow:
Visit the official website of UPSC, and search for the admit card link.
Click on the admit card link and read the instructions given.
Click on “Yes” and after that click on the link “Forget RID”
At this stage, a new page will open which will ask you your particulars, such as, your Name, your father’s and mother’s name, your date of birth, and of course a captcha code will be given for final submission.
Upon filling in the details, you must click on the submit button.
Click on it and what you were seeking will be at your disposal. Your IAS Registration ID will be re-generated.