Download the TemperatureMonitor library from following link.
Unzip the library and copy to the Arduino libraries folder. Program compiled and tested successful on Arduino 1.8.12.
Now, open the program from File -> Examples -> TemperatureMonitor -> TemperatureMonitor.
Compile and upload the program to NodeMCU. Connect your mobile device to NodeMCU and open 192.168.4.1 in a web browser.