You are in your first year of the O-A visa.
IF a Thai border opens and you can exit and reenter before December 2 you woulf be stamped in for one added year.
However that appears doubtful...due to COVID.
SO in order to extend the OA inside Thailand...you will need to visit your immigration office and get their list of requirements to do so.
Likely will find the need to meet the financial requirements of the one year Extension of Stay. If your Embassy provides an affidavit of income...get it. Or show 800,000 Thai baht banked in your name only Thai bank.
You will need to have a health insurance policy which meets the 400,
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,000 Thai baht requirements purchased from an approved Thai insurer.
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