How to flash firmware to linkit 7688 dual without wifi and usb

I'm using mt788 linkit smart duo and I have flash wrong firmware to the board. So I cannot upgrade or flash new firmware to the board through wifi web local (there is no wifi interface anymore) and usb otg too.
Anyone know how to flash linkit's firmware again for this case.
P/s: I have flash openwrt 15.05 to the board without linkit feed.

if the bootloader still works for serial port, maybe you could flash the code by serial port.

If the bootloader dead also, the only way is using a SPI programmer to write a new bootloader code into the IC directly.

Hi, do you know how to flash by serial port or spi ? Is there any post or blog talk about this?

serial port method, check your board / bootloader support Docs.
Programmer: google CH341A spi programmer .

Thank you, I will try your method and inform here soon