Programming flash by using external flash memory

Hi dear friends,
I'm trying to program Arduino DUE microcontroller by using an external storage. In this case, I have hex file programmed before using Arduino IDE, and copied it on SD Card so when Arduino DUE microcontroller connected to power supply, self programmed by that hex file (or pressing a button).
What solution do you prefer?

The Due is a Von Neumann machine, maybe you could bypass flash and load programs into RAM. Not sure if this is helpful...

You know, I want to program the microcontroller by using a firmware file uploaded on SD Card, not by using a programmer connected on a device such as a computer.
As I know, first memory thay CPU gathers information from, is Flash (contained compiled program). So how can I define another flash memory instead of main microcontroller?

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Does it need a specific library or Arduino programmer configuration?

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I just wanna research and find a best solution.
Would you mind if you tell me what should I learn about, please?