you should be applying for the non O in your home country before you get to Thailand. That will make getting a bank account much easier and you don't have to worry about converting from a tourist visa to a non o.
yes, the app said I had to go to the bank to change. Possibly because I had opened the account on a tourist visa last year. So I updated my visa information at the bank in 30 minutes but needed my Sim card receipt which they sent to headquarters. My new number was approved in 5 days and I could then simply change it in the app. A lot of variables and everyone's situation could be a little different. That was just my experience. May not apply to the op if he was already on a long term visa when he opened the account
You need to get th receipt from your carrier for your new number and take it to the bank. I did this 2 weeks ago. They send your information in and it takes 5 days to validate your new number at my bank. They sent me an email saying I could now use my new number. I use Bangkok bank. May be different at other banks.
Maybe I read that wrong, did your phone number change?