1. Download and install the ST Link utility from ST on a Windows computer: https://www.st.com/en/development-tools/stsw-link004.html
2. Obtain the “upgrade hex file” from ToltHawk support and save it into your local hard-drive.
3. TURN OFF the ToltHawk device and connect it via USB cable
4. Launch ST Link utility. 
5. In ST Link Utility, select File -> Open to  Open the saved hex file
6. Turn on ToltHawk device. If the device’s lights don’t flicker, the device is in sleep mode and you’ll need to turn it off and wait up to 5 minutes and repeat this step
7. Now that the device is ready to be programmed, click on the “Connect to Target” menu in ST Link Utilty. This should detect the device. If the device isn’t detected make sure that step 6 above is performed correctly and the USB cable is attached to the device
8. In ST Link Utility, click on “Program Device”
9. In the following UI dialog click on the “Start” button. This will reprogram the device
10. Upon Successful programming you’ll see the below message in STLink Utility:

08:22:59 : Device family :STM32L4x3
08:23:00 : Memory programmed in 1s and 750ms.
08:23:00 : Verification…OK
08:23:00 : Programmed memory Checksum: 0x003C5968