First off you don't have an O-A visa anymore (if you ever did) as those can only be gotten from a thai consulate in your country or in a country you hold legal permanent resident status.
Secondly you can NEVER EVER "renew" any visa.
What you have is a yearly extension of stay based on being over 50.
Be that as it may. The requirements in Chiang Mai are pretty much the same as everywhere except they are rabid about you having filed a TM.30 form with them.
That's the form with the oh-so long name of Notification From For House-Master, Owner, Or The Possessor Of The Residence Where Alien Has Stayed.
Other than that you'll need the same documentation you used in Bangkok to get a yearly extension.
Here is what a yearly extension of stay stamp looks like. I'd bet dollars to durian you have this and NOT an O-A visa.