The ESP8266 WiFi chip on the standard OS 3.0 does not have a plug for external antenna. If you need to connect an external antenna, you can request a version of ESP8266 chip that has external antenna plug — we do have some of these chips available and can replacing the stock ESP8266 chip with these special ones.
You can submit a ticket and return the current one you have, and we can replace its top board (the main controller board) with one that has external antenna connector.