I used a generic CP2102-based USB to serial adapter from eBay. Any 3.3v-level serial/UART adapter/device should be OK.
Connect GND from the serial adapter.
Short the RX pad on the sensor to GND. This triggers the bootloader.
Connect 3.3v from the serial adapter.
Remove the RX pad to GND short.
LED should be solid red. If it isn’t, then this method will not work.
Connect the TX/RX from the serial adapter to the “T”-marked TX pad and the RX pad next to it.
Downloads and install Flash Programmer2 from TI.
Flash Programmer 2 (select the serial port, then CC1310F128)
You can also backup your own firmware using this tool and command
cc2538-bsl.py -p com10 -r -l 131072 backup.bin
credit goes to Mr. Null from WYZE forum