Don´t understand how to install evcc image to Nanopi R3S eMMC

I have flashed the EVCC R3S image to a micro-SD card. If plugged into the R3S, it boots from the SD and EVCC is ready.
But how do I flash the image onto the eMMC of the R3S?
If I remove the SD-card, the standard FriendlyWRT is loaded.