You can find the Re-submit button -- Open the App >> Go to Orders Page
Manually resubmit the orders to send them to AMAZON.
After turning off the order sync button, you can validate the orders manually as per your wish before sending/ syncing them to Amazon FBA via an option to "Re-submit to Amazon" in the order log.
For past orders, you will get the status of all the orders as "Pending" once imported in our app, and you need to re-submit/archive the order as required under the order log page.
Refer to the link for the Import Order feature: