Contact your FASTag issuing bank or FASTag provider
Log in to the bank’s FASTag portal or mobile app
Go to the profile, account, or customer details section
Select the option to update mobile number
Enter the new mobile number
Verify the new number using OTP
Submit the request
If online update is not available, visit the bank branch or customer care
Carry your FASTag account details, vehicle details, and ID proof if required
Ask the bank to update the registered mobile number in the FASTag account
Wait for confirmation from the issuer after the update is completed