Need Help with Tax Documents from Vietnam and Thailand for U.S. State Tax Filing

Hey everyone, I’m in a bit of a tricky situation and could really use some advice. I was working in Vietnam and Thailand for a number of years but, as a U.S. citizen, I’ve recently been informed that I still need to file state taxes back home. However, I’m having a hard time figuring out exactly what documents I need to obtain from the overseas countries I've worked in and how to submit them properly to the U.S. state tax office.

The state where I'm registered as a resident isn’t providing much help—they keep sending me links to sections of a PDF without actually answering my questions. Has anyone been through this before and could offer some guidance on the steps I need to follow? Specifically, what documents should I get from Vietnam and Thailand, and how do I ensure they are acceptable for U.S. tax filings?

Any help would be greatly appreciated! Thanks in advance.