The STM32 firmware uses the Arduino IDE, you'll have to add Maple boards support and select "Generic STM32F103C" or "Maple (Rev 3)" IIRC. You may need to install an older Arduino IDE (I'm on 1.8). This should help you getting started: https://github.com/rogerclarkmelbourne/Arduino_STM32/wiki
Extract NonBlockingRTTTL library in the "library" folder of the Arduino install.
If the Arduino IDE doesn't see the device automatically, try plugging the USB as soon as the orange lines come up in the IDE log window, timing is a bit critical. Also make sure you have the relevant DFU drivers if you're using Win.
I also attached STM32_complete.bin in case you mess up the bootloader. This file is the complete dump of the STM flash, and must be flashed with an SWD programmer on the specific pins.