By default theme will show a copyright text in footer. Format of this text is:
© YEAR SITE NAME, All rights reserved.
How to Show / Hide footer copyright text
Footer copyright can be managed from theme settings page.
Navigate to:
Home 
Administration Appearance Appearance settings Edu X
example.com/admin/appearance/settings/edux
On this page, you can show / hide copyright text.
Custom Copyright Text
This feature is available in Edu X Pro theme. You can read more about Edu X Pro and purchase this theme from here:
Edu X Pro - Premium Drupal 8 , 9 Theme