Check the manual for a way to remove 'Image Retention'.
If it doesn't have anything that's easy to find, set the input to Tuner and go to a station that doesn't exist, so it shows 'snow' which you may have seen when the tuner wasn't on the correct channel with no programming. Leave it that way and go out for lunch, a run, shopping, whatever- let it go for about an hour and check to see if the image has been reduced.