TL;DR: In the vast majority of cases, what looks like a double charge is a failed payment authorisation followed by a successful one. The first amount will drop off automatically within a few days.
What usually happens
Your payment provider sends an authorisation request to your bank. If that first request fails, they try again. Sometimes both attempts appear in your transaction history before the failed one is released. If one of the charges is marked as pending or on hold, it has not been captured and will return to your account without any action needed.
We want to stress that our company itself does not provide payment/transaction services, that is done by Amex/Stripe/Mastercard/Visa etc.
What to do
Wait a few days and check again. In 95% of cases this resolves on its own.
If seven days have passed and the second charge is still showing, contact us and we will look into it with our payment provider.