How do I add an accommodation for individual students for existing quizzes?
Without knowing exactly what type of accommodations you're specifically looking for I may not be answering your question fully, but I will do my best.
You can use the moderate quiz option to give a student an extra attempts (Once I publish a quiz, how do I use the Moderate Quiz page? )
You can also use the assign to option in the quiz settings to assign the quiz to individual student(s) to the quiz early or extend the availability of the quiz (What options can I set in a quiz? )
Hopefully one of these quiz options is what you're looking for.
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