When you're asked to confirm it's you, just open your app and tap on the bell icon on the homepage. You'll see the notification to confirm it's you. Tap it and follow the instructions. You'll see the details of the transaction and you'll be asked to confirm it's you. Once you've confirmed it, your transaction will be updated.
It's easier when you have notifications switched on. You'll find this under 'More', 'Settings', then 'Enable push notifications'.