Hello I think that you have one choice if you must have a pristine display; you have to replace it. There are replacements available online. You might be able to DIY this one but, you could probably also bring the replacement to a phone repair shop and they would do it for you. Sadly there aren’t any guides available on ifixit.com but there are YouTube videos about this. You can get displays on websites like this : https://www.parts4repair.com/complete-screen-assembly-for-oppo-f1s-white/
Or in short you can’t fix the display you will have to replace it. Or get a new phone this phone is 9 years old so kudos for keeping it so long,
-Totoro