Install OpenWrt 18.06.x on MT7688

Hi friends,
I want to install openwrt 18.06.x on Linkit MT7688. it seems that there isn't any official ROM for it. how can I do that?[Model*~]=7688


How can I have access to .img file? or how can I install the OS on the module? do you have any guidance document? based on linkit "developer's guide" I should have .img file to install using a USB stick.

I follow the instruction by Upgrading OpenWrt firmware from the Command Line and the link you have send.
but during upgrade the processor stops working and wifi led is on continuously.