Hi. The Seller Help Center, as so often, has the answer: see the “Note” bit at the end.
When an order is marked as Incomplete, the buyer is still required to submit the requested information for the seller to complete the order. The order status cannot be adjusted until the buyer replies to the seller’s instructions.
As sellers, you can leave this section blank if you do not require any further information.
You will also see an option to send a reminder to the buyer, to notify them to reply to the instructions.**
A buyer will see a message indicating a reply to the instructions is required to start the order.
Note: After a week has passed from the original order creation, a seller can cancel the order without any harm to their cancellation ratio or ratings.
So, you can keep reminding, or cancel.