I found a strange line after posting my first topic

that can happen when you type your post in a program like microsoft word, and copy and paste it into your forum.  Did you do something like that?

Yes, I typed the text first in a word document, and later I pasted it into the topic.
 How can I delete this error? Should I delete the topic and rewrite it?
Chief, thank you for the explanation!!

you can edit the post, delete all the content in the post and rewrite it within the post.