As a first step, please make sure that your booking is still within the editing / free cancellation window.
When can changes be made?
up to 60 minutes before the pickup time for one-way rides under 200km
up to 24 hours before pickup time for one-way rides over 200km
up to 24 hours for by-the-hour bookings
If you are still facing issues after confirming that your ride is editable, the reason could be a removed payment method. If this is the case, you will need to cancel the booking and place a new one with the correct payment method.