Why iphone 6s frequently restarts?

I have an iphone 6s with 76% battery health. the problem started, when it got frozen and touch screen didn’t work.so I held the power button to restart my phone. when it got restarted, while booting, a horizontal white line appeared in my black screen then it turned on. Now I am having a problem with it. It randomly restarts with the same white horizontal line. what can I do about it?

Thanks a lot

Take it to Apple. It's a 5-year-old phone with hardware problems. Apple will agree to replace the battery when the health is below 80%. The charge for a battery replacement is quite small.

If there are other problems, then you may want to save your money and think about an upgrade.