If your students really make a mess of things after starting Banqer but making silly transactions or something similar don't worry you're not the only teacher to experience this. In fact it's somewhat expected as your students stretch their financial wings.
Sometimes though things get in such disarray it's easier to start again. In your 'Settings' we've created a handy button for this situation. If you scroll down to 'Reset all transactions' you'll be able to do exactly this. Have a read through before unlocking the danger zone as this can't be undone.
This means that you don't have to create a whole new class adding your students and groups again. Hopefully it helps you if you ever need it.