Where are SPI DTB Overlay files?

Hi, I have a need to enable both SPI0 and 1 via overlay files. However, I have not been able to find any such overlay files in the Kernel or U-boot build directories nor in the Armbian file system. I can also not find any uEnv.txt file that various documents refer to on this file. So I’m lost.

What are are the step-by step instructions for enabling both SPI ports on Radxa-Zero?

Thanks,
/John.