Exchange rates for employment salary

Hi, I earn a monthly salary and get paid in Hong Kong dollars. When submitting PAYE, I convert the Hong Kong dollars into sterling pounds using HMRC monthly rates for NIC purposes. But for tax purposes, I reported nil as I intend to file a Self-assessment return. So my total salary appeared in my P60 is zero. Now I am filling in the SA return, I would like to ask if I can use different rates, such as HMRC average year rates or spot rates, for the conversion of my monthly salary. Many thanks and looking forward to your reply soon.

Under the terms of Self Assessment, we do not provide an official exchange rate and the onus is on the individual to use a just and reasonable exchange rate for each acquisition and disposal.
You are free to use any of the three rate HMRC provides, or you can use a rate obtained elsewhere, such as a newspaper or the London Stock Exchange.
For your convenience, there are exchange rates at: The National Archives: Exchange rates from HMRC in CSV and XML format

For older rates at: The National Archives: Foreign exchange rates and spot rates: 1 January 1989 to 31 March 2009
You are free to use any of the supplied rates or one of your own choosing