To unlink your GCash account from your Apple services account, you must go to ‘Payment and Shipping’ on your iOS device and do the following steps:
Click or tap ‘Remove’ on the payment option you would like to remove (Your GCash account in this case)
Tap Remove to initiate removal of GCash as Payment Method.
A page will pop out, click or tap ‘Remove’ at the end of the prompt.
GCash has now been unlinked from your Apple services account