To withdraw your funds, you would need to transfer the funds from your Stocks account to your Bamboo Wallet.
You can do this by clicking on Portfolio Breakdown under Stocks on your Home page and then click on "Transfer to Bamboo Wallet". It may take some time for the money to move from your Stocks account to your Bamboo Wallet.
Once the money reflects in your Bamboo wallet, you can then proceed to withdraw your funds.