What Documents Are Needed for a COVID Visa Extension at Muang Thong Immigration Office?

Hello, my coworker and I (US Passports) both work in China and can't go back (boarders closed).We already extended our Visas the first 30 days. The visa exemption expires on April 10th. We would be going to the immigration office near Muang Thong. The huge building one. We both have the COVID letter from the US Embassy. Does anyone know the necessary documents needed for the COVID extension at that immigration office? As well, is it possible to go in the afternoon to this location? We both work online in the morning. Any experiences at this immigration office not arriving at 4am-10am? Thanks in advance!