The first card that you add to your Google Pay app automatically becomes the default card. To change your default card:
Open the Google Pay app.
Find and select your Viva Wallet debit card at the top.
Tap “Make Default”.
For all countries, including those that do not yet support Google Pay, you can set up your Viva Wallet Digital Debit Card as your default Google Pay card through Google Pay Service (Settings-> Google-> Account Services- > Google Pay).