Just connect a network cable to the modem and the first floor.
You mentioned having a wired connection on the first floor already, so what exactly is your question?
Thanks for your response. I have a wired point on the 1st floor so I want to connect a wifi router there to have good connectivity. The signal of the router on the ground floor is weak and gets disconnected frequently. Hope I am made my question clear.
Thanks
Anirban
Then use a ‘normal’ WiFi router you can buy in a store, not a modem/router. Connect your modem with a network cable to the new router WAN port.