Reset or deleting joplin

It depends, any particular text in Joplin?

Also how familiar are you with CSS (Cascading Style Sheet) code?

For instance if you want to justify the main body text displayed in the Markdown editor render pane, you need to add the below code to userstyle.css

body {
  text-align: justify;
}

If the above doesn't make that much sense to you, have a read of this wiki page which is intended as an introdution to customising Joplin using CSS.