@lsimmons11
If you are using New Quizzes, then you can reopen the student assessment. This lesson from the Canvas Instructor Guide explains how: How do I moderate a student's assessment attempt in New Quizzes?
Given that you mention Respondus Lock Down and it doesn't work with Canvas until July 18, 2020, and that your new attempts wiped out their answers, you must be using Legacy Quizzes instead of New Quizzes.
The ability to do this with Legacy Quizzes was a feature requests here in the Community. Canvas has stopped development for legacy quizzes and the announcement that the ability to reopen was completed only applied to New Quizzes (called Quizzes.Next at the time). There are several places where their solution requires people moving to New Quizzes to get it.
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