You obviously have permission to stay until August 2020. Follow the stamp I’m your passport and you can’t go wrong.

The key to this process is you need to have at least 15-20 days left on your tourist visa or visa exempt entry and you must have your original degree, not a copy.

Please note visa on arrival is not the same as entering with no visa at the airport. For example Chinese get a visa on arrival and Americans get a 30 day stamp visa exempt entry. So if you got the visa exempt entry at the airport, you can get 1 normal 30 day extension. This is what I think you have based on your name. Therefore, no TM30 is required. Form name is TM7