Tutorial : https://www.instructables.com/id/Arduino-Robot-Car-Bluetooth-Controlled-and-Program/

This app is designed to make it easy for you to build a basic Wifi robot car. The app allows you to control an ESP8266 based robot car over Wifi (on AP/STA mode), and also you can upload Arduino sketch/code directly from your Android phone to ESP8266 via USB OTG or Wifi OTA (Over-theAir).\n\nPlease be advised that this app contains ads and potential in-app purchase to improve next app development.

Features:
- Simply remote control interface
- Upload firmware via USB OTG or WiFi OTA directly from Android phone
- Remote control mode
- Obstacle avoidance with servo mode
- Line follower mode
- Object follower mode
- Available Arduino source code