@binhen this is an English forum, so please try to write in English language.
What I have translated, you want to change system on your eMMC module.
You have two ways:
- run system from microSD card on your Rock Pi and write image to eMMC from within that microSD system
- use adapter to connect eMMC module to PC and on PC you can write any image from within Windows or Linux system
If I use the first method, how can I set up the SD card to start the system?Because the existing EMMC card also has a system。
You can write image provided by Radxa to SD card.
This operation should be no problem. When I write this SD, will it start automatically from SD card? Because the EMMC of pi4b also has a default system on the board. Or do I need to switch startup items?
Try yourself. If system starts from eMMC then erase it and system will start from SD card.
For rk3399, uSD card has a higher boot priority. If there is a bootable uSD card, it boots from uSD card first, if not, then look for bootable eMMC.