Clone this repository into your kernel source tree, e.g.
$ cd nethunter_a21s
$ git clone https://github.com/BasGame1/nethunter_kernel_a21s.gitcd into kali-nethunter-kernel/, open config and make sure that you are happy with all the settings.
Important: Changes should not be made in this file. Copy it across to local.config and delete everything except the parameters you would like to change. Change those parameters and save it.
The settings in local.config overwrites config but will itself not be overwritten by updates.