Your Quibi subscription is billed directly through your Apple App store or Google Play store, depending on the device you were using when you signed up for Quibi.
For Apple App Store users, change your preferred payment method by following the instructions here.
For Google Play Store users, change your preferred payment method by following the instructions here.
To switch between Apple and Android billing, check out our "What happens if I switch between Apple and Android?"
If you have questions about a subscription you received through your employer, please contact support.