I'm here to make sure that you'll be able to disconnect your bank to QuickBooks Self-Employed. Let's perform some troubleshooting steps to sort this out. This way, you can delete the bank connections in QBSE.
There are times that the browser stores frequently accessed data, thus causing QBSE to act weirdly. Let's try logging in to your QBSE account using a private or a different browser. Press this shortcut key on your keyboard to open a private browser:
Press Ctrl + Shift + N on your keyboard for Google Chrome and Mozilla Firefox.
Press Command + Shift + N for Safari.
Once logged in, try to delete bank and transaction data again to double-check. This way, you'll be able to delete the bank connections.
Additionally, I've also added this article to make sure that your transactions are under the correct account, you can easily categorize them in QuickBooks. For the detailed steps, please visit this article: Categorize transactions in QuickBooks Self-Employed.
Please post a reply below if you have other concerns with your transactions in QuickBooks Self-Employed. I'll be more than happy to assist you again. Have a great day and take care always.