I really need your help.
I connected the dht output to 0 pin mc23017.
What should I write in DHTPIN?
DHT dht(DHTPIN, DHT22);
You're using an I/O extender?
The DHT library doesn't know anything about I/O extenders.
That is, I can only use it to flash the LED?
The DHT sensor can not flash an LED.
The DHT sensor can not be read through a port extender of any type that I'm aware of.
I talked about mc23017.
That should be the MCP23017 (there's no such thing as an MC23017), and it can do a lot more than flashing an LED.