What should I tell immigration about my overstay due to Covid in Thailand?

Hello all

I hope this is the right place to ask.

We’re flying home next week. We had to change our flight date due to having (mild) Covid. We confirmed it by doing some home ATK tests and self-isolated for 10 days. I’m aware of the fact that we’ll be charged a fine for overstay.

Upon investigation, what do we say to the immigration officers? Should we just tell them we had to extend our stay because we had Covid? Would they ask for proof that we had it? I’m a bit worried because we never went to the doctor and don’t have a recovery certificate and such.

Thanks in advance.