I appreciate you taking the time to reach out in the Community and share your request about adding Class by batch. Let me help share some insights about this feature.
This is easy and possible if you add an accountant as a user in QuickBooks Online. They can use the Reclassify Tool to find transactions that have been assigned to incorrect accounts or classes and reclassify them in batches. Since this is only available for QuickBooks Online Accountant subscription, I'd recommend inviting an accountant to be your best work partner for this.