wdt.h is included on Arduino IDE.
This example show how it's work:

#include <avr/wdt.h>

int counter=0;
void setup(){
   wdt_disable();
   
    Serial.begin(9600);
  Serial.println("Starting...");
  delay(1000);
 
  wdt_enable(WDTO_8S);
  
}

void loop(){
  wdt_reset();
  
   Serial.println(counter);
   counter++;
   
   if(counter==5){
      while(true){}
   }
   delay(500);
  
}```