Which file is specified for the U-Boot image in Chapter 4.3.4 of imx_linux_users_guide (Rev.L5.4.47_2.2.0)? The board uses iMX8M mini.Specifying u-boot-imx8mmevk.bin did not boot on the board.
sudo dd if=<U-Boot image> of=/dev/sdx bs=1k seek=<offset> conv=fsync
Try to burn uboot again:
sudo dd if=<uboot-image> of=/dev/<path to your sd> bs=1024 seek=33
If you can not seen it is working, try to compile and rebuild uboot and make sure that your sdcard is erased.