You have two options to get your second account to show up for reconciliation.
First, you can go to the Reconcile page and make sure you select your second account from the Which account do you want to reconcile drop-down. Then, enter the ending balance and the ending date to start reconciling. I'll attach a screenshot below for your visual reference.
Second, you can go to the Bank register and click Reconcile. Then, enter the ending balance and the ending date from your bank statement and start reconciling. To do so, please follow the steps below:
In your QuickBooks Online (QBO), click Accounting from the left menu and select Chart of Accounts.
Find the second account you want to reconcile.
Click View register under the Action column.
On the Bank Register page, click Reconcile at the top right corner.