I went through this process a couple months ago, because I got tired of going to different banks trying to find one that didn’t require it. The form you need is an affidavit. It can be found here:
You will also need to schedule an appointment with your embassy. Depending on which country you’re from this can be easy or take some “squealing” to get an appt. When I did mine the US Embassy wasn’t allowing appts, but if you lobby and tell them you need for a bank account and visa, they will grant you one - I had to bitch a bit to get my appt. There is a $50 (USD) fee (US Embassy). I would bring any additional documents you have that are relevant, like WP or ED visa to Bangkok bank as they may or may not ask for it.
I got mine via email (it’s on their website) at a time when they were only granting emergency appointments. I needed an affidavit for a thai bank account. I have to bitch and whine a little before they finally granted me an appointment. Don’t just accept no for an answer.
you don’t need a WP. I opened account with BKK Bank off amnesty and used it to apply for my retirement visa. They asked for WP, but I told them that makes no sense as I can’t work if I have a retirement visa. You have to push back on them when they try to deny you. Many clerks are lazy or don’t fully know the rules.
