Currently, the only way to update the credit card on file for any product created in GoHighLevel is to go into Stripe, and enter new CC info for your customer. This means you'll have to call them up, ask them to give their credit card info over the phone, and then manually type it into Stripe.
In Stripe, there is a way to natively send people a link to update their CC info, but GHL doesn't utilize it, and it is disabled in Stripe (see attached image).
My feature request would be to add a "Send Link to Update Card On File" or "Update Card on File" option under the "Action Dropdown" on the subscriptions tab, payments tab, and transactions tab. When you click on this, you would see a pop-up with two options: update manually or send customer a link to update. From there, you could either enter new CC info or send the customer a link to add a new card.