We want to disconnect our Amex cards from QB. Can we bulk transfer all of the transactions on the dashboard(500+) to an Amex unallocated account and classify ourselves?

I've got ways to bulk transfer all your transactions on the Dashboard to your Amex Unallocated account in QuickBooks Online (QBO), Nking.

First, you'll have to ensure all your transactions are matched or added to your bank register, Any transactions left in the For Review tab will be deleted when you disconnect the bank feed, resulting in lost, unreconciled data.

Once the transactions are in the bank register, you can then use the Reclassify transactions tool to transfer them in bulk from there original account to your Amex Unallocated account. This tool enables you to reclassify multiple entries in batches, saving a significant amount of time and effort.

However, please take note that this functionality is only available in QuickBooks Online Advanced and QuickBooks Accountant. If you're using QuickBooks Online Plus, Essentials, Simple Start versions, you'll have to reclassify those transactions manually.

For those with access to QBO Advanced, you can locate the Reclassify tool by navigating on the Settings icon at the upper right corner of your Dashboard. From there, you'll have to look under Tools, and select the Reclassify transactions option.

If you have an accountant associated with your account, you can have them use their QuickBooks Accountant version to handle the reclassification. Their expertise can also help to keep your books accurate and compliant with relevant regulations. 

Alternatively, you may also consider upgrading your account to QBO Advanced for self-service access to the Reclassify tool.

You can refer to this article for further information: Reclassify or Move Multiple Transactions.

Feel free to reply to this post if you need further assistance.