No, once that jpeg damage is done, it's done. You have to start again from the raw image.
PLEASE read: https://www.damiensymonds.net/2010/02/trash-those-jpegs.html
Well, if your external screen was perfect, then yes, you'd want them to match Since it's not perfect, I held high hopes for the laptop one
Let's go back to that 6500 error thing. I need you to do this.
Oh!!!!! I didn't know this! I should have looked at your sidebar, and I would have figured it out.
Can you confirm you have the external screen set to "Extend" not "Duplicate" in the Display Control Panel?
And? Is 83 good? Got a good brightness match now?
This is annoying, but shouldn't matter, because once the calibration begins, the whole screen is filled with colour, isn't it?