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The board should be able to flash over UART. Use the GPIO9/PWM1 pin header and pull it low during chip reset (which can be done with the on-board button labelled ESP_RST). This will put the ESP32C3 in Joint Download Mode.
Use PWM5/6 as UART receive/transmit, respectively. Alternatively, the GPIO18/PWM3 and GPIO19/PWM4 pins can be used for USB-Serial-JTAG Download Boot.
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