Make an AUD withdrawal via the 'Withdraw' button. Tap the blue 'AUD Account' card on the dashboard, and tap 'Withdraw' up the top right.
AUD withdrawals are made from your AUD wallet to your linked bank account. If your funds are still in BTC, you'll need to sell the BTC in your account via the 'Sell' button on the dashboard.
AUD withdrawals are free. Make sure you have linked a bank account and completed Bank account verification to be able to withdraw.