Bank Account linking.

I don't think there is any facility on the gst portal for linking of bank account.
Bank account details are entered only once i. e. just after obtaining registration.

Yes there is no need to link the bank account. you have to provide the bank details while registering. Refunds if any will be processed to the said bank details

As per notification 31/2019 of CENTRAL TAX dated 28 June 2019, new rule 10A was introduced which states that taxpayers are req. to furnish bank account information on portal within 45 days of grant of registration or the due date of 3b whichever is earlier.

Now, after logging into GST, you have to go to amendment in non core field and provide the bank details such as acc number., acc type and copy of bank statement etc.

Trust this clarifies
In case you req any help, contact me on 8989066636
Regards,
Nihit