Someone has asked a friend of mine that he wanted to extend his tourist visa and  obviously went to Immigration office and they asked him for proof of funds and as far as I know came in on a normal tourist visa.
He is not married to a Thai and think no one can help him and obviously has no Thai bank account.
Any advise appreciated.

It is very unusual for Immigration to ask for proof of funds when doing a standard 30-day extension of a tourist entry (including visa exempt). I suspect he was looking for a 60-day "Covid" extension, rather than the virtually 100% automatic normal 30-day extension. If a normal extension, he should check into a hotel in another province for one night, and apply for the extension there. If he is looking for a "Covid" extension, someone here can probably advise on a good immigration office to use if we know his current location.

 

There is an outside chance he might be on a Special Tourist Visa (STV). Special conditions apply when extending that, and the issue might be that he could not show the required insurance.

As for a tourist visa from Seoul, I have not seen any recent reports. However, the rules back around 2018-2019 were that you could, in principle, apply. However, they would refuse to provide a tourist visa to someone who has recently been in Thailand as a tourist.

Is your friend a Korean citizen? If yes did he enter visa exempt and get 90 day stay under a bilateral agreement.

If not Is he on a tourist visa or did he enter visa exempt?