You are required to file using either married filing jointly or married filing separately. Yes, you can amend, the instructions are here.
https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...
If you file jointly, you must declare and pay tax on all your combined worldwide income. If your spouse is overseas and earns income overseas, this may mean paying tax on the same money twice, although there is an offsetting deduction. Depending on where your spouse lives, what their income is, and if they also pay taxes overseas, you may want to file married filing separately or jointly. It depends on your exact situation and there is no one size fits all answer.
