One of the ways you can assign payments to expense accounts in Reconciler is by manually filtering to display a set of payments and defining what account all of those transactions should be assigned to.
Step 1 - Go to "Reconcile" view
Step 2 - Find the specific payments on the right portion of the screen that you want to assign (Use any necessary filters)
*Example: Searching for "Microsoft Bing Ads"
Step 3 - Click the "+" sign to expand filter option for Payment
Step 4 - Use the drop down to select the account you would like to assign the payment to and then click "Set"