How to help a dementia patient to fill up SA form

Hi! I have a question about filling up the self-assessment form for my father, who retired and has an old age allowance from the HK government. He became a tax resident starting from the 2022 tax year and needs to report the self-assessment in the 2023 tax year. Unfortunately, he had a head injury after a stroke and become a dementia patient since April this year. He became lack of ability in self-care, communication and judgment. In this situation, as his daughter, how can I help him to complete the self-assessment this tax year?

Hi
You would need to obtain Power of Attorney in order to act on his behalf :
Make, register or end a lasting power of attorney
Thankyou.