Here is a summary of how you remove GCash as your payment method in the App Store:
STEP 1: Open your Settings
STEP 2:Tap your Apple ID
STEP 3: Tap Payment and Shipping
STEP 4: Tap GCash
STEP 5: Tap Remove Payment Method
STEP 6: Tap Remove
You have successfully removed GCash as a payment method for your App Store account. You will receive an SMS to confirm the unlinking of your GCash with your App Store account.