Once you have moved to Nest, your User ID is your PAN and not your earlier User ID or nickname.
To know how to set up your login for the first time refer to the link below:
How do I set my Nest password?
Which number will I get an OTP on if my numbers are different in trading and DP?
I did not receive any OTP while resetting my password
Are Neo mobile app and Nest logins different?
I forgot answers to the security questions?