The VE.Bus System Configurator is installed with VEConfigure3.
From
https://www.victronenergy.com/support-and-downloads/software
VE Configuration tools for VE.Bus Products
This package contains:
- VEConfigure 3 (v9004236)
- VE.Bus Quick Configure (v9010154) - For installations up to 3 Multis
- VE.Bus System Configurator (v9009154) - For larger installations
- VEFlash (v9005163) - Firmware update tool to update VE.Bus products
If you have been downloading VEconfig files from VRM, editing them and then uploading via VRM, you already have the VE.Bus System Configurator. It is more commonly used to configure multiple parallel inverters. You can initiate the firmware update from this same computer. Since you have a single inverter, you will likely only see VEConfig come up.
MK3-USB comes with one or the other. USB-A is the most common.
USB-A plugs into a common USB port like on a PC.
USB-C plugs into a recent Android phone.
So if you can plug your MK3-USB into a PC, you can install and run VC on the PC and do the firmware update following the same steps in that video, except with the PC version.
This video shows the MK3-USB with USB-A, and shows updating with the PC version: