I haven't watched that video, but I'm familiar with PDF tutorials that don't work.
First off, I'm using the kernel from git.linaro.org/landing-teams/working/qualcomm/kernel.git. If you're using something different, then your mileage may vary with the following.
I use a command like the following to bring up menuconfig:
$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- \
If you get an error about not having that compiler, you can apt-get it under Debian "stretch":
$ sudo apt-get install gcc-aarch64-linux-gnu
NOTE that you'll almost certainly have to do the above under Debian "stretch", since older gcc's don't seem to like the Dragonboard kernel sources. (There are probably additional compiler suppliers, i.e. Linaro.)
After you get the configuration how you want it, instructions similar to those at the following link will get you a kernel image, modules, and so on: