Please see the readme of this project on Github.

This is a DIY project for our itracker boards, after you do the following step:

You will see the DIY UI as follow:

Then you can select any components to compile according to the hardware you want to use like RAK8211-NB.
BTW, there are some documents for hardware of RAK8211-NB, and you can refer to them:
http://docs.rakwireless.com/en/Cellular/RAK8211/Hardware Specification/RAK8211-NB Datasheet V1.0.pdf
http://docs.rakwireless.com/en/Cellular/RAK8211/Hardware Specification/RAK8211 iTracker_NB_Brochure(V1.0).pdf