Certificate of residence in the UK - after having left the UK

Hi everyone, I am an Italian citizen and have lived and worked in the UK circa 2015-2017, and have moved to Denmark since. The local tax authorities are now asking for proof that I have lived in the UK during 2015-2017. I am considering of requesting a Certificate or residence, but I couldn't understand if it possible to do so retroactively (i.e. as a non-british citizen who doesn't live in the UK anymore). I have tried the online form on the HMRC website, but that seems to require identity verification specifically asking for a UK-issued document which I don't have. I have also found this form: https://www.tax.service.gov.uk/shortforms/form/PT_CertOfRes which could work for me? I would only need a letter or document that states that I was living and registered in the UK for the aforementioned period. Also, do you have an estimate of how long it would take to receive such a certificate? Unfortunately the deadline for submitting this evidence is quite tight. thank you and kind regards

Hi,
You can request a letter of confirmation of residence for a period in the past here:
How to apply for a certificate of residence to claim tax relief abroad
You should specify the dates it is requried for, the country that needs it and that it is for tax purposes.
Thank you.