Borrowers affected by the loan book sale received a letter on 15 November from Metro Bank to let them know their mortgage would be under new ownership.
NatWest says it will be sending welcome letters to homeowners on Monday 22 November.
After 19 November, Metro will no longer own the mortgages. Brokers acting for any borrower whose mortgage has been transferred to NatWest and are coming to the end of their rate can request a product transfer with NatWest and be paid a 0.20 per cent procuration fee.
NatWest is introducing a temporary paper product transfer process until Feb 2022 before the digital solution is available. The form can be found in the bank’s A to Z library under product transfers.
The gross value of the loans being taken over by NatWest is more than £3bn and represents a third of Metro’s mortgage book.
The sale completed on 2 February.
A NatWest spokesperson said: “We are pleased to welcome our new customers to NatWest and look forward to offering them great service and value.
“We’ll be writing to customers directly to advise them of what this transfer means for them. Customers will see no changes to the terms and conditions of their mortgages. We are committed to offering a range of products and services to help customers get the best deals and help them make their homes more environmentally friendly.”