How To Write A Letter To The Bank Manager That I Am Giving Authority To My Father?

Your address and date
Dear Sir,
Your name as shown on the account and bank account reference number
I hereby authorise my father XYZ of (address) to sign this account on my behalf and I enclose a copy of his signature, passport copy, and local address details.
Please confirm when you have regularised this action
Yours faithfully
Signed
Your name

Be prepared to have to go into a bank personally with your father to verify this!