You can set up your Tap to Pay card through your Zip app:
1. Log in to the Zip app and go to the 'Pay' tab
2. Make sure you have selected 'Instore' at the top right of the screen
3. Once you have activated your card, click 'Add to Apple Wallet'
4. Follow the prompts to add the card to Apple Pay
(you will need to verify your card with a one-time password via text message)
Here's a video to show you the steps: