Can anyone teach me how to display CSV file data into the dashboard ( for example, a line chart )

Go to the hamburger menu on the upper right of the screen and click on it. Select the 'Export` option. Click on 'all flows' then 'Copy to clipboard' and then paste it into a reply.

When doing the paste, it is important to surround your code with three backticks
```
like this
```

See this post for more details - How to share code or flow json