Change Portfolio Item Slug

Install and activate the child theme.
Go to Dashboard > Appearance > Theme Editor and open functions.php file. Or you can edit it via FTP in wp-content/themes/bizix-child-theme directory.

Add the code in the functions.php file:

function custom_portfolio_slug() {

return 'portfolio-item';

}

add_filter('gyan_portfolio_slug','custom_portfolio_slug');

Change "portfolio-item" text in above code with your custom text.
Go to Dashboard > Settings > Permalinks and Save changes without editing anything. This is needed to refresh the permalinks so that the new changes take place.