@hube2 I came up with an alternate solution using a Search and Replace plugin (Better Search Replace by Delicious Brains who now owns ACF of course!)
I did a search and replace on the wp_usermeta table for the typo and replaced it with the correct spelling. I then went into the checkbox field setting and fixed the typo. After that I checked any users who had the typo selected and their choice had updated (and remained checked)!
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