How do I remove a fixed line from an imported graph

I have imported an excel graph with an added line into this graph.
In LibreOffice this line seems to be fixed.
I can not find a way to delete this line.

Please upload your ODF type sample fele here.

I have made ods files. I seem not be able to upload them

Use the Up-arrow:

I am sorry; I just started using LibreOffice.
I have no idea how I can get this bar to be able to upload.

It is not a LibreOffice related feature.

The up-arrow icon is in this site at the top of the message editor box. Click on it, then browse the sample file in yout storage device. Select it.

I do not use messenger at all.
Besides I decided to create new ods files from my excel sheets after leaving out these lines, which I can not remove in LibreOffice.
A bit more work, but already done.
Now I can add the lines in the ods files.
Thanks for your help

You have wrote a MESSAGE (an ANSWER) some minutes before. I said that small editor-window of THIS SITE.

Thank you kindly for your help.
I have solved my problem by starting all over again without having the lines in my diagrams.
As far as I am concerned my question is solved.
Thanks again

Note the little envelopes in the upper right of the posts by @Ducky1951 I guess he is not using the same interface as we ( website ask.libreoffice.org ).
.
Maybe:
How do I use Discourse via email? - FAQs - Mozilla Discourse

Follow the following link with your Web-Browser and you should find your thread.

When you log in you can use the speech bubble to the lower right to answer on a post. The editor wich opens will have the icon for upload wich was shown by @Zizi64