How to fix flickering screen

@luiggi10769 without seeing what is going on and just going by your description, this sounds like a failed display.

Since iFixit doesn't yet have a guide for this, use something like this video to work on it. Replacement screens are readily available at many online stores. Pick one close to your geographic location.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.