To follow
@T**
's instructions, You need to get the latest requirements list from the Chiang Mai immigration office for each step.
All below is general information, NOT the Chiang Mai version.
(1st step). You can check with this as a reference for your in-country Non-O visa based on being over 50/retirement
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/9.FOR-RETIREMENT-PURPOSES-50-YEARS-OLD-NON-O.pdf
(2nd step). You can check the attached as a reference for your 1-year extension based on being over 50.