Have a read of this: https://wiki.libreelec.tv/development/git-tutorial
In short, you need to create a diff patch that patches the kernel sources either modifies the x96-max dts file or (better) adds a new dts file for your box. Clone Linux kernel sources from https://github.com/chewitt/linux/commits/amlogic-6.1.y then create a new branch and make and then commit changes. You can then generate the diff patches from the commits (git format-patch ..) and copy them into the LE buildsystem at projects/Amlogic/devices/AMLGX/patches/linux/ then rebuild the image so the patches are applied to kernel sources and included in the built kernel. If you modify the kernel build folder direct; a) respinning the image will not pickup the changes, b) if you force the kernel package to be rebuilt this will remove the build folder and unpack it again from sources overwriting your changes.