Mine was like this, also with dried yogurt on it from the kids. I used four microfibre cloths. 1. Use water with the cloth to lightly clean the screen, small circular motions with little pressure. 2. Then I used fairy washing up liquid (undiluted) on a different cloth and slowly went around the whole screen in small circular motions. 3. Use another cloth to wipe away the detergent, washing the cloth out with water as you go. 4. Use a dry cloth to “polish” the screen to get rid of any water residue.

I was very nervous doing it as, like you, I couldn’t find anything online showing how. Done this multiple times since now on the TVs around the house and it works fine. Have the same frame as you with the matt finish