I don't understand which platform you are using. It's either Jira Cloud or Jira Server.
If you're using Jira Cloud, this can't be done. I mean you could try to reopen the sprint just to close it again, but this would close it with the current date/time and not a specific date/time.
If you're using Jira Server, then you could modify the database directly to change this. There is a KB on this in How to edit the Dates Associated with a closed Sprint. However this change requires you to directly modify the SQL database Jira is using, an action that is not officially supported. It probably won't cause any problems to do this, but I would still recommend that you create a fresh backup of your database before you try to make this change. I would also recommend that you stop Jira before changing this SQL entry. This way once the SQL change is done, you can simply start Jira and that way all the internal caches about this should be cleared by the restart.
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