I'm trying to help a friend, he has listened to the visa agencies in stead of me in the past so now he think he is "up the creak without a paddle"...
 

When he got his non-B visa in the past, the school he is working for had not applied for all documents (their first foreign teacher!) so in the end he could not get a WP and make the extension on his non-B on time. So he just went for tourist visa until it should be all solved (now on his second tourist visa as he didn't do an extension on the first visa as the visa agency recommended him to get a new visa instead...). Now the school has all documents needed (as far as I know) but the visa agency now told my friend that he can not get a new non-B visa or change his tourist visa to a non-B as he already had a (1) non-B visa connected to that employer so therefor he must either change employer or passport. I believe that he should be able to either obtain a new non-B from Laos or change his tourist visa at Changwattana but he don't believe me as the the visa agency say another thing. 
So who is right the agency or I?!

Utter nonsense from the agent. There is no rule that states that only one non-b can be issued for the same employer.

He could apply for a change of visa status at Chaeng Wattana if he is living in Bangkok. If not living there he has to apply at his local office.

Requirements are here for change of visa status. https://www.immigration.go.th/content/service_73

 

I am sure your friend is aware that working as a teacher with a tourist visa entry, regardless of what an agent or a school might say, is working illegally. Maybe a new school/agent are the best option.