Hi sir, I think you should fly to Guangzhou or Shanghai from Singapore firstly and then transfer to Zhengzhou by air, too. When you arrive at Zhengzhou, you could take a train or a bus to arrive in Xinyang quickly.

For the flight and train information, you could search the details respectively at:
https://www.travelchinaguide.com/china-flights/
https://www.travelchinaguide.com/china-trains/