Power of Attorney added - what next?

Hi I recently had my POA added to my mother's HMRC records. The problem is, I've no idea how I move forward. I need to do her self assessment. She has a UTR but no online service set up. She has Alzheimer's and is in a care home. I can't locate her passport or proof of ID. How do I add her to my account so I can do her SA online?

Hi,

For assistance please contact the online helpdesk:

Technical support with HMRC online services

Thank you.