Program your board using the esptool.py program, found here.
To put the TinyC6 into 'download mode', hold the BOOT button while connecting the USB cable. It can be released after the connection is made.
If you are putting MicroPython on your board for the first time then you should first erase the entire flash using:
esptool.py --chip esp32c6 --port /dev/ttyUSB0 erase_flash
From then on program the firmware starting at address 0x0:
esptool.py --chip esp32c6 --port /dev/ttyUSB0 --baud 460800 write_flash -z 0x0 UM_TINYC6-20240602-v1.24.0.bin