Hello Heathhud13.
Thank you for using Apple Support Communities. It sounds like you have some Starbucks gift cards in the Wallet app and would like to know if you can transfer the balance on those cards to the Starbucks app. Allow us to share some information with you. Each card and pass that you add to the wallet app have their own information and settings that you can change. While having the Starbucks gift card open in the Wallet app, select the more button on the top right. This will allow you to view all available settings and information. Just in case, please review the resource below:
How to use Wallet on your iPhone, iPod touch, and Apple Watch - Apple Support
Review the section under "Choose pass options in Wallet". If you don't see an option listed to transfer funds, then this will not be possible. You should still be able to use the Wallet app to pay for items at participating Starbucks.
We hope this information is useful. Cheers.