What is the process to change my visa from a Non-B to a Non-O related to marriage with a Thai national?

you will need to fulfill the financial requirements when you change the reason for your extension from work to based on marriage with a Thai

You don't get a Non-O visa, you're already on an extension of stay and all you'd do is change the reason for the extension

IF you will still be employed and do it when your current extension of stay is expiring instead of applying for another extension based on employment you apply for one based on marriage to a thai by meeting the requirements

IF you are going to quit your job you get documentation from your employer saying you stop on xxx date, go to the immigration office cancel your current extension based on employment and apply for a new yearly extension based on marriage.

Either way go to your immigration office and get the hand out listing the requirements needed to apply for a yearly extension based on marriage to a thai so when you go to change the reason you have the paperwork you need to do it