1. Go to the Login page of GST Portal

  2. Click on Forgot Username

  3. Enter the Provisional ID or GSTIN or UIN. Enter captcha code and click on Generate OTP

  4. Enter OTP sent on registered email or mobile. Click on Continue

  5. Username is sent to the registered email

  6. Use the credentials to login to the GST Portal.

Read step-wise process - GST Portal Login : Forgot Username