Try a bootable sd card. If the u-boot in eMMC is still good, it should boot from that.
If the eMMC u-boot is bad, then you'll need to open it up and move the eMMC switch, then it should be able to boot from SD.
If the eMMC u-boot is bad, then you'll need to open it up and move the eMMC switch, then it should be able to boot from SD.