First, don't leave feedback until all aspects of the transaction are completed so you are not in this situation. Feedback is NOT intended to communicate to your trading partner. You message the seller, and then if necessary you exercise your rights under the Money Back Guarantee or the seller's Returns Policy for that listing, and only after all that you rate and comment on the ENTIRE transaction.
You can apologize to the seller for your premature feedback and advise the seller that you would gladly revise the rating and the comments if s/he would send you a revision form. A seller can only send a VERY limited number of such requests each year so s/he might not want to use one up for you.
You can alternatively post a follow-up comment (giving specific dates, especially for when delivery was estimated at the time you paid vs. what date you left the feedback and when you actually received the item) to what you left by going to your own Feedback Profile--click the "(20 ⭐)" in your post header--then click on the Left for Others tab and there should be a link under the When column.
