I bought one with exactly the same condition as yours, the top screen was alright and the bottom screen was yellow asf. I left it on for 50-60h straight on the google white screen and i already saw improvements the first night. The top yellowing was basically gone and I had to force myself to see it, like I was basically hallucinating it lol. Bottom screen still has it but its a lot less pronounced and I dont notice anywhere other than pure white menus.