@Lyndon ******
follow Ellie's advice. IF you went to the cham Churi Square immigration office to get that extension you go BACK there (with documents from your employer to cancel both the extension and the work permit)
THEN you would slog on over to Chaengwattana immigration office and apply for a 60 day covid extension (assuming you're going to be able to pull this off before the 29th when the current covid extensions run out AND taking into effect there are holidays on the 26th and 28th this month)