Need guidance on CFW for O3ds 6.2.0-0U

I recently purchased a 6.2.0-0U 3ds which has never been online since the browser demands to be updated before I could use it (and I know I shouldn't update any higher). I want to know how to get rxtools on it. I have a Sky3ds blue button with Cubic Ninja and a ds flashcart that works on the 3ds.

I have tried the ninjhax exploit but they don't have a QR code for the -0U firmware. It starts at -7U which I'm not quite sure how to get to...

I have tried the rxinstaller.nds MSET exploit for...

Need guidance on CFW for O3ds 6.2.0-0U