If a credit card is declined, or something else happens you may need to register someone manually for an event.
If they have already tried to register - you can find them in the event roster
Just to to the event page and use the big blue "Edit" button to the right of the event title. The arrow to the right gives you a list of options including the event roster
Find the person you need to change and use the details button on the right to find the "Pay by Check" option
Use this to record the payment
THEN, use the SEPARATE Notes field at the bottom to write in the transaction # from Stripe
In this case you would put the transaction ID in the payment notes as shown below