WooCommerce Currency Switcher — Fixed Price of another currency

Hi all,
I am currently using Hong Kong dollars (HKD) on my page and my products are displayed in HKD. But now I want to include Taiwan dollars (TWD) in my website so I want to set a fixed price in TWD for each of my product.
I did some research and people said it can be done by switching on the ‘Individual Fixed Price Rules for Each Product’ in WooCommerce>Setting>Currency>Advanced. But I cannot find this function on my back-end.
Anyone know how to troubleshoot this problem?
Thank you!