Reply To: Enter predefined text in searchbox

[Tom]

You can overwrite the entire function in your child theme:

if ( ! function_exists( 'generate_navigation_search' ) ) :
/**
 * Add the search bar to the navigation
 * @since 1.1.4
 */
add_action( 'generate_inside_navigation','generate_navigation_search');
function generate_navigation_search()
{
	$generate_settings = wp_parse_args( 
		get_option( 'generate_settings', array() ), 
		generate_get_defaults() 
	);
		
	if ( 'enable' !== $generate_settings['nav_search'] )
		return;
			
	?>
	<form method="get" class="search-form navigation-search" action="<?php echo esc_url( home_url( '/' ) ); ?>">
		<input type="search" placeholder="YOUR PLACEHOLDER HERE" class="search-field" value="<?php echo esc_attr( get_search_query() ); ?>" name="s" title="<?php _ex( 'Search', 'label', 'generatepress' ); ?>">
	</form>
	<?php
}
endif;