You can change your mobile number in TGB bank by following these steps-
Visit a TGB branch and ask for the KYC form.
Fill in the KYC form duly, where you will have to fill in details like- account number, account type, account holder name,
Tick the box which you want to change, here it will be changing mobile number.
Write the new mobile number you want to register.
Put the signature wherever required and submit the form.