How to change the email subject for Contact Form notification message?

Follow the next steps in order to change the email subject:

1. Open your WordPress admin dashboard.
2. Make sure that Contact Form plugin is installed and activated.
3. Navigate to Contact Form Settings page.
4. Find and open "Additional settings" tab.
5. Find "'FROM' field" and make necessary changes in "Name" and "Email" sections by selecting appropriate radio buttons and setting the information.
6. Save changes and check the result. 

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Additional resources:

How to Use Contact Form - Step-by-step PDF Instruction