Hi S Lam,
You will need to undertake the residency tests, which can be found at Residence, domicile and the remittance basis: RDR1
, to determine if you are taxable in the UK for the whole tax year or the period that you were resident in the UK.
If you are deemed resident in the UK for the whole tax year, you will need to complete a self assessment tax return (SA100) and enter your Hong Kong income on the foreign page (SA106). If you are deemed as resident for part of the year, you will then need to determine if split year treatment applies.
If it does apply, you would need to complete a SA100, SA106 declaring foreign income received after the date you arrived in the UK and S109 residence page.