How do I change contact details using a lasting power of attorney

I wish to change my father's contact details to my address as I manage his affairs under a lasting power of attorney (LPA). To where should I write? Does HMRC need me to obtain an access code to the Office of The Public Guardian's record of the LPA so that you can effect the change or do they already have access? I do not have access to any Government Gateway account he may have had (he has dementia so cannot assist) and HMRC's phone lines are too busy.

Hi Mark,
You would need to send the original or certified copy of the power of attorney to:
Pay As You Earn and Self Assessment,
HM Revenue and Customs,
BX9 1AS UK.
Thank you.