Part of the screen touch is not working.

@daviandawson "dead spot" on a touch screen are almost exclusively an issue with the screen itself. Of course, you can always check the ribbon cables. Ultimately it sounds that your issue is the touchscreen and you will have to replace the display to repair this. Use something like this video as your guide.

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.