It’s pretty rare, but it has been known to happen. It’s happened to me once in the year that I’ve been on Fiverr. Not much to do about it. If it’s an active order, just message the buyer and explain what happened. Or request a mutual cancellation on the condition that the buyer can provide the order details to keep the order open. The way I fixed the problem is by editing my gig and re-writing the instructions. Be careful when you do this, though, that you click all the buttons that have to be clicked. If I remember correctly, you have to save the order instructions in the box where you enter them, and you also have to confirm the change with a second button lower on the page. It’s not elegant.