Hellow Rishabh.

If you have filled your aplication till document uploading stage then don't worry. At initial satge you had submit your mail. Just go through the same website for which you are applying. There you will find a option forgot user ID,click to that option enter your mail id. A confarmation mail will sent to your respective mail id. Check your mail and they will ask some questions like DOB etc. Then they will send you your User ID. By following this process you will be able to retrieve your user ID.