The MT7688 chip was not supported in official 14.7 releases. You must have some manufacturer's custom built firmware.
For support of that firmware, contact the manufacturer.
Looks like the source might be available at https://github.com/MediaTek-Labs You should confirm that it is the proper software for your board, perhaps from the vendor of your board.
"Best" would be confirming with that source that the hardware and flashed firmware is the same as what mk24 linked and moving to current, supported OpenWrt.
Building from that source might also be possible.
Note : LinkIt Smart 7688 uses the MediaTek proprietary Wi-Fi driver. While OpenWrt Chaos Calmer is evolving, only selected Linux kernel versions of it are supported by the Wi-Fi driver (3.18.21 ~ 3.18.44). If you are looking for a non-proprietary Wi-Fi driver, the mt76 project would be a reference of the choice.