How to use extern kernel

I have a imx6ul board, and I have find a github repo for imx6ul and openwrt [kerner v4.19] and I have a kernel that can work but version is lower. v4.1

when I use git.rootfs and my zimage ,it can work ,but kerner version is different , when i insmod ko, it will tell me error.

so I want to use extern kernel , or how to change the kerner version ?