There are two methods:
1 Change the text in the core files:
* Search an replace text in frontend_review_form.html in the folder wp-customer-reviews\include\templates
* deactive and reactive the plugin
You will loose the changes when you update the plugin
2. Change text with Javascript:
If you have jquery support (if not add in the head)
Add custom js in your footer:
$(“div.wpcr3_button_1.wpcr3_show_btn”).text(‘YOUR NEW CREATE A REVIEW TEXT’);