How can I apply for a 1-year extension of stay on a Non-Immigrant (O) visa in Thailand?

You go to your immigration office and ask them for their list of requirements to apply for the 1 year extension. Each immigration office has their own requirements, so you need to ask the immigration office in the province you are in.

All of the Non-O 1-year extensions requirement you to have a Thai bank account and a certain amount of money in them, varying from 400,000 baht to 800,000 baht.