If tickets have already been sold, you are able to switch your payout method to a different Stripe account. To do so, hop into your Payouts Tab and click "Change Payout Method".
This will not affect any transactions processed using your prior Stripe account.
However, if a ticket was purchased with any other payout method before setting up Stripe (even if it was a test and was refunded), you won't be able to use Stripe for that specific event.
In this case, your best course of action would be to duplicate the event to reset your payment options, and then direct guests to this new page. If needed, you can even keep the same URL. Just make a little change on the original event's URL to free up the one you want, and set it for the duplicated one!
Check out Can I reuse a previous Splashthat domain for a new event? for more details.