Where should my cousin apply to cancel his visa and extend his stay in Thailand after resigning from his job?

The user is inquiring about where their cousin should apply to cancel his visa and apply for an extension of stay after resigning from his job, highlighting that the cousin's extension was based on employment and that he needs to process his current employer's paperwork. Commenters suggest he should go to the immigration office where he originally received his extension, specifically mentioning the Chaengwattana office for those in Bangkok.