iPhone SE -- Stocks App
One thing to try is add a few more stocks and then the chart should be off screen. Also, when you tap on a specific index - it should take over with the appropriate chart.

If all the indexes are wrong, you might need to remove them and re-add what you need to see if the settings for the app are messed up somehow.

You can delete this app entirely and re-install it as well, so that's kind of a last resort item to try.