you do as Benjamin Hays told you. You'll need to go to the labor office first and cancel your work permit. Then, you can cancel your one year extension of stay based on employment, and apply for a 60 day extension of stay based on unable to travel due to COVID-19.
he is from the UK, his embassy doesn't make up the affidavit, so he needs his Thai bank give him the letter, i.e. documents which prove 12 months of transfers from abroad into his Thai bank account over a minimum of 40,000 THB every month
I smell some discrepancies. How could he have been issued a Non-Imm-O visa based on marriage on 15th of June in his home country, entered Thailand after this date and only being issued an extension until 16th of May LESS than one year later?
you are qualified for visa-exempt entry. But you still must obtain the COE. You will have to apply online and follow their instructions. Need health insurance, ASQ hotel booking, flight details, and the PCR test to board the flight etc.
for the applications to the 1-year permit of stay based on being married to a Thai, he needs to fulfill the financial requirements, which are either a deposit of 400,000 THB on a Thai bank account or proof of monthly income of a minimum of 40,000 THB