As above, please?
...and how it relates to maximum attempts?
'reopen' means that the student's graded submission will be archived in the history of attempts they have made on this assignment and they will be allowed to submit a new attempt (at the point when they do this, they will be given the option of using their existing submission as the starting point for their new submission, or if they want to start afresh with a blank submission).
The maximum attempts is the maximum number of times this can happen.
This is not to be confused with the situation whereby students do not need to submit their assignments for marking, so they can continue to edit their current submission as many times as they like.
Thanks (and I did confuse those two things).
I'm not sure you can infer what the 'reopen' facility does from the help and/or documentation.
I'm always cautious that different practices or simply exact meaning of words between different English speaking countries can often be at play here.