Link for add board manager

http://arduino.esp8266.com/stable/package_esp8266com_index.json

Erase the esp

esptool.py erase_flash

Code to flash AT firmware to ESP8266 (ESP8266_AT_Bin_V1.5.1)

esptool.py --baud 115200 --port /dev/tty.wchusbserial1420 write_flash -fm dio -ff 40m -fs detect 0x00000 boot_v1.7.bin 0x01000 user1.1024.new.2.bin 0xfc000 esp_init_data_default.bin 0x7e000 blank.bin 0xfe000 blank.bin