If you purchased the SX pro, then you have jig and the usb c dongle which you insert jig and the usb dongle to switch.
Download SX Pro 1.9 unzip the boot.dat to the root of sd card.
hold volume + and press power one time
it will boot to SX menu, you can turn on autorcm and generate lisence-request file
and then you go to https://sx.xecuter.com/
to activate the license and download the license.dat and put it on the root of the sd card.
however, if you didn't buy sx pro or paid sx license... you better go youtube search ReiNX tutorial....
the tegrarcmgui is for switch in RCM mode connect to PC and inject the payload if you dont have SX Pro Dongle
The whole detail instruction in on https://sx.xecuter.com/