I appreciate you taking the time to reach out to us here. Reconciliation can be a lengthy process but don't worry, I'll be happy to provide the necessary resources required for you to complete your reconciliation with ease.
Based on the message you're getting, it's essential to make sure your bank account is connected to QuickBooks. For reference, here's an article that shows you how to: Connect bank and credit card accounts to QuickBooks Online. In case you're getting the same message after connecting to your bank, I recommend accessing your account using a private/incognito browser window. This is a great way to bypass most browser-related issues.
In the meantime, feel free to check out these articles with more info about reconciling: