If you have forgotten your Gmail id, you can restore it by selecting the Gmail Forget option
In which you may need all these things
Gmail id (Never mind the password, no matter what) you select the option for forget
If you do not know your Gmail too, you can do this by entering your registered mobile number.
When you enter your register mobile number, then the one-time password will come in your register mobile number.
As soon as you enter that password you will be allowed to create a new password.