Hello there,
First of all, thanks for using eVision Corporate Pro theme.
To change the button text you have to do some code customization, on ‘about.php’ file inside ‘inc\hooks\front-page’ directory on theme folder, the code where you will have to customize is at line 85.
Note: Child theme is recommended for code customization.
https://codex.wordpress.org/Child_Themes#How_to_Create_a_Child_Theme
Hope this will help on resolving your issue.
Thanks!