You can override ad Submission form and do your necessary customization
Copy the following folder or specific files from this folder as you need
Source Folder and Files: #
wp-content/plugins/classified-listing-pro/templates/listing-form
Destination Folder and Files: #
Copy the folder or specific file to your theme or child theme
wp-content/themes/your-theme/classified-listing/listing-form
Files need to edit
Form: form.php
Information: information.php
Contact part: contact.php
This are several part here you can edit which part you need.