Let me share some information so you'd be able to successfully reconnect your bank with QuickBooks.
Just to clarify, what is the name of the bank you're working on? This is for me to further check on the reason why you're unable to reconnect it.
In the meantime, you can try reconnecting your bank using a private browser or an incognito browser. This way, we can isolate the prompt you've received for possible browser-related. Here are the keyboard shortcuts that will help you accomplish this in all supported browsers:
If it's working fine, go back to your old browser and clear your browser's cache. This process will clear up cached-related issues. You can also access your account through another browser.
On the other hand, here's how to reconnect your bank account:
Go to the Gear icon.
Choose Bank accounts under Transactions.
Click the Connect another account menu.
Enter the name of the financial institution or the bank's URL in the Search box from the Connect another bank or credit card window.
From the list, click on the name of the account you’re working on.
Look for the name of the financial institution from the list.
This will take you to the Sign in to your bank screen.
Follow the on-screen instructions to complete the process.