Vontar x3 Amlogic s905x3 4GB RAM GB LAN Damaged ROM

How install CoreELEC at SD card (USB pendrive)?
Terminal rs 232:
LOOP:11;EMMC:800;NAND:81;SD?:20000;USB:8;
Terminal rs232 with reset button
SM1:BL:511f6b:81ca2f;FEAT:A0F83180:20282000;POC:F;RCY:0;EMMC:800;NAND:81;SD?:20000;USB:8;

I downloaded sm1_s905x3_4g_1gbit and what’s now?

CoreELEC installation instructions, step by step guide and video tutorial.

You killed the eMMC, it’s empty or damaged.
Use Amlogic USB burn tool or Burn card maker and restore your vendor Android image first on the device.

https://wiki.coreelec.org/coreelec:aml_burncard
https://wiki.coreelec.org/coreelec:aml_usb_tool

Memory burned down - damage.

Try this, and if that doesn’t work, then please contact the device manufacturer for repair or replace the unit with a functioning one.