Hi Howard,
I hope you are well today and thank you for your questions.
The search form and its placeholder text are displayed by the theme that you are using on your site so you can change it by editing theme searchform.php file in the child theme as described in the following page.
How to create a custom search form in WordPress
Alternatively, you can change the text by translating your theme or using any of the below plugins.
Say what?
Real-Time Find and Replace
We are going to implement these options in the future version of the plugin so that you can change it easily.
Best regards,
Ivory Search Support