How to set my iPhone to Taiwan store so that I can recharge my Taiwan iTunes card in it

The support article Change your Apple ID country or region - Apple Support describes how to change your country setting on everything using your Apple ID, and the requirements and results of doing this

Changing store country is not a trivial endeavor. The system is set up to only facilitate doing this if you are moving to the other country to take up residency. It makes it difficult for people to temporarily change country settings to do things such as get around distribution restrictions only allowing them to buy items available in the country where they live.