@sr15673: First of all you will need to create a child theme. For that you can use the Generate Child Theme Plugin. Activate and use this plugin to create a child theme of your Clean Education Pro Theme.
After creating the child theme, go to the child theme folder and open functions.php file and add the following
code.
add_post_type_support( 'page', 'excerpt' );
After adding the above code you will find the excerpt check box option in the Screen Options when you go to Edit a Page.
Then you can check the excerpt option and you will find an excerpt text area below the page content.
There you can put in the text you want to display as excerpt for the page.
This way you can achieve different excerpt length or text for different page.
Let me know if you have any doubts regarding this.
Regards,
Skandha