Here is a summary of how you update your payment method on Google Play Store to GCash via web browser:
STEP 1: Open your browser and go to Google Play Store App
STEP 2: Click your Profile icon
STEP 3: Click Payments and subscriptions
STEP 4: Click Add Payment Method
STEP 5: Click Add Payment Method
STEP 6: Click Add GCash
STEP 7: Click Continue
STEP 8: Open your GCash app and scan the QR code
STEP 9: Click Authorize
STEP 10: Enter the 6-digit authentication code sent to your registered mobile number. Tap Next
Congratulations! You have successfully added GCash as a payment Method for your Google Play Account. You will receive an SMS to confirm the linking of your account.