Can I use my custom file system on SD Card

I made own AArch64 filesystem using yocto.
and make EXT4 partition on SD Card
and copy the filesystem.

There is no boot partition on bootargs or cmdline.

So how can I use my SD card partition(ie. /dev/mmcblk1p1) as boot partition
instead of default Android system partition.

You might get some clues from:

I put my custom rootfs in the on-board flash but the proceedure (based on compiling a kernel with a command line built in) should be the same for rootfs on SD card.