@Shea ******
You would go to the labor department and cancel your work permit. You'll then go to the immigration office and cancel your extension of stay based on employment. When you cancel your extension of stay based on employment, you have until 11:59 PM *THE SAME DAY* to leave Thailand, OR to apply for another extension. The Thai government is selling a 60 day extension of stay based on unable to travel due to COVID-19, that will let you stay for another 60 days. The last day they are selling it is March 30, 2021.