how to add dynamic footer credit in Greatmag theme [closed]

With out knowing the theme personally it’s not easy to tell you exactly what you need to do. However, as @WebElaine has pointed out, the code you will need to change will most likely be in your themes footer.php file.

It’s not recommended to edit themes directly and you should, instead, consider using a WordPress child theme – https://codex.wordpress.org/Child_Themes

If you have a child theme setup and activated, you should then copy the footer.php file from your ‘parent’ theme to your child themes folder and edit the file where you want your copyright notice displayed.

In order to display the copyright notice as you requested you would need to use something like the following code:

&copy; 2000 - <?php echo date('Y'); ?>