Head to your 'Pending Bets' section and click on the green cash out symbol. Click 'Full cashout' and then 'confirm'. The funds should go straight into your available balance.
Step by step...
Head to your 'Pending Bets' section within the PointsBet App, locate the bet you wish to Cash Out.
Click the green Cash Out symbol.
Click 'Full Cash Out'.
Click 'Confirm'.
You should now see the Cash Out value reflect in your account balance.