How can I successfully apply for a COVID-extension at Chiang Mai immigration?

Quick COVID-extension successful report:

I arrived at 10:15am at Chiang Mai immigration at Promenada Mall. I asked to apply for a COVID-extension, they said ok. My current TR30 (US-passport visa exempt, already extended once) stamp runs out in a week, and they tried to convince me to come back a week later, but I said no thanks, it's fine, I'd rather do it today. Okay, no problem - they helped me fill out the forms, made copies for me for free, and even wrote my address (which is in Thai) for me on the form since it would have taken me three times as long. I walked inside, no wait at the counter, handed the stack of papers and 1.9k THB over; 5 minutes later, I had my passport back with "Under Consideration" stamp to come back on March 21. Left around 10:35am.

This is first, and most likely the last, time that I'll get the COVID extension, although I had a 90-day stay (TR 60-day + 30-extension) in Q3-Q4 2022 as well.

Cheers!