Hi @emorgannn
Thank you for posting your question in the community! Technically, you can not backfill people into the flow due to the event trigger of Fulfilled Order, which is based on a real-time trigger.
However, you could create a segment of people who have recently fulfilled their order in the last 90-days, clone the message within the flow, and send to that segment as a campaign to request any of your past customers to write a review.
You would just want to make sure as part of your segment, you exclude anyone who has already received your Review Request email from the flow.
I hope this helps!
@In the Inbox