I need help transferring data from one console to another using one micro sd card! (Reupload)

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I have 2 modded 3DS's, one a New 3DS Xl (current) and a standard New 3DS (want to use). I want to know if its okay or if theres anything specific i need to do to transfer all the files from my New 3DS XL onto my computer, format the sd card then put the files from my XL onto the New 3DS I plan to use? If you're wondering why im asking this or why i dont have another one is because I only have one, 128 gb sd card and buying another one is expensive for me at the moment. I need help since I'm confused and I dont want to lose all my data please.