People just ask a question and we answer based on our experiences, which is all we can do,
As I'm sure we all know having dealt with different offices, one rule doesn't necessarily fit the other. I know here in bangkok is different from Chiang Mai.
Don't use an agent it will cost you 10 times what it should.
Jump onto the Thai government website I'm sure you will find the relevant information there and download the paperwork. Email to the employer, I think that would be the easiest way if you are not in Thailand