How do I write a kernel to an SD card?

[Tom Trebisky <tom%mmto.org@localhost>]

I have an SD card set up to boot NetBSD 9.3 on the Orange Pi PC plus I 
have here.
As I recently reported, this will boot NetBSD, but does not run well.

This morning I built NetBSD from the latest sources (from Git) and it 
says that it is
NetBSD 10.99.2  I would like to copy this kernel onto the SD card I have 
here and
give it a try, but don't know how to do that.

I am using linux as my build system, and that seems to work well.
I can plug the SD card into a USB card reader and mount the first partition
(which is a FAT partition, presumably for EFI booting).
Is there some way to copy the kernel I just built into this partition or 
is this
entirely the wrong way to go about things.

My apologies if these are dumb questions, but I am new to NetBSD in this 
day and age.

Thank You.