How to restore uboot back into my IPQ4019 box


I got a "G-DOCK" wireless router which is a Chinese brand I think.
it has an IPQ4019 soc inside with a 16M nor, and 128M.

It is a second-hand one. And it has an "Opboot" as the bootloader of it.
// I checked the Opboot, it has a web-based, it is convenience for most of the time.
but I am trying to install my firmware by following the document, and the uboot commands are using in the document.
So, my question is "How to install the original uboot back into the box?"

Thanks in advanced.