First, it's not possible to brick those devices by flashing a firmware.
You can find firmware for all Boyue devices,
https://www.mobileread.com/forums/sho...d.php?t=265289 Latest is the 160620 one. There is firmware for T61C if that is your model.
You have to flash through a computer obviously, see
http://radxa.com/Rock/flash_the_image
I use both upgrade_tool and rkflashtool on Linux (I don't use Windows at all), both work fine.