Since RoboKiller subscriptions are handled by the Google Play Store, all payments are made from the card linked to your Google Play Account. 

1. On your Android phone or tablet, open the Google Play Store app .
2. Tap Menu  Payment methods  More payment settings.
3. If asked, sign in to pay.google.com.
4. Under the payment method you want to edit, tap Edit.
5. Make your updates. 
6. Tap Update.