Firstly, you and your (ex) partner would need to arrange a property settlement, in terms of orders by consent, or a Financial Agreement.  This is the document that the bank needs to see, to show them that you have binding and enforceable terms relating to the transfer of title and payment of money, and also so they can see that you will qualify for the exemption of stamp duty.
It is not a 'letter from a lawyer', but documents that both parties have signed off on, and made in final and binding terms.  The stamp duty exemption on transfers of property between separated couples only applies if there is evidence of family court orders made, or a Financial Agreement entered into between the parties.
Secondly, you take the finalised consent orders or Financial Agreement to the bank, and arrange for the settlement of the transfer of title and payment in exchange.  That part is basically a conveyancing process, just as if you were selling a house, except that the parties are you and your ex partner, and the 'contract' is the family law agreement reached between you.
To start the process, we suggest you start with an consultation where we can review the details of your settlement, and explain these procedures in more detail. Then we are able to advise you about the costs and steps involved in drawing up terms of settlement, which would be sent to your ex partner, for them to review  with their own solicitor.   If agreed, they then would then have to sign the terms and return them for you to sign.