When you use your personal SpendAble card to pay, the money in your 'default wallet' will be used when you tap your card, without having to do anything in your SpendAble app.
If you wish to pay from a different wallet, simply select the wallet from the drop down list on your SpendAble app home page.
The wallet which will be used when you tap your card will be visible in the grey box above the drop down menu.