I'd like to know why you weren't able to reconcile your bank transactions with QuickBooks so that I can identify the cause and provide you specific resolution. For now, to trigger the connection between QuickBooks and your bank you can select the Update button in the Banking menu. Here's how:
Go to the Hamburger icon and select Transactions or Banking menu.
Click the Update button located on the top right corner of the page.
If you're not able to see the transactions from your bank after waiting a few minutes, you can manually enter your transactions in QuickBooks. Here's how to import your transactions to QuickBooks Online (QBO) :
Log in to your bank website and download your transaction within the date range.
Review the format to CSV, QFX or QBO file.
Import the bank transactions by going to the Gear icon.