• In your Arduino IDE, go to File> Preferences

• Enter https://dl.espressif.com/dl/package_esp32_index.json into the “Additional Board Manager URLs” field . Then, click the “OK” button:

• Open the Boards Manager. Go to Tools > Board > Boards Manager…

• Search for ESP32 and press install button for the “ESP32 by Espressif Systems“:

• That’s it. It should be installed after a few seconds.

  
  

  Note: if you already have the ESP8266 boards URL, you can separate the URLs with a comma as follows:

  https://dl.espressif.com/dl/package_esp32_index.json, http://arduino.esp8266.com/stable/package_esp8266com_index.json

Links:

For ESP32 https://dl.espressif.com/dl/package_esp32_index.json
For ESP8266 http://arduino.esp8266.com/stable/package_esp8266com_index.json