Contact Form 7- Fatal error!

Hi,
When I was istalling the Contact From 7, a error happened, and that moment I can’t see the site.

How I can uninstall the pluging or to resolve this problem.
I can’t use my backend only appear this screen:
Whoops \ Exception \ ErrorException (E_ERROR)
Call to undefined function wpcf7_add_shortcode()

———————-
Whoops
\Exception
\ErrorException
/home
/nexusimagen
/public_html
/GALATEA
/wp-content
/plugins
/rich-text-editor-field-for-contact-form-7
/classes
/class-cf7rt-rich-text-editor.php
28

———————-
28. array($this,’rich_text_editor_shortcode_handler’), true );
29. }
——————————————–
Please anybody could help me?
I need to edit the site.
Thanks
Julia