Good to see you here in QuickBooks Community. I'm here to help and provide some insights about updating Customer's credit card in QuickBooks Online (QBO).
As of now, there isn't an option to set a notification if when will be the upcoming expiration dates of your customer's credit card. For now, you can update your customer's billing information anytime to avoid any interruption when accepting credit card payments from your customer.
While this option is currently unavailable and I can see how this feature would be helpful for you, I recommend sending feedback directly to our product developers for the future update.
Here's how you can send feedback:
Click the Gear Icon.
Click Next and choose Feedback under Category option.