copy searchform.php from parent theme to child theme and you can make you edits inside this file.
Line number 10 contain Search for, you can replace with your own.
<?php
/**
* The template for displaying search forms in Boss
*
* @package Boss
*/
?>
<form role="search" method="get" id="searchform" class="searchform" action="<?php echo esc_url( home_url( '/' ) ); ?>">
<div class="search-wrap">
<label class="screen-reader-text" for="s"><?php _e( 'Search for members, events, social groups:', 'boss' ); ?></label>
<input type="text" value="" name="s" id="s">
<button type="submit" id="searchsubmit"><i class="fa fa-search"></i></button>
</div>
</form>
I will close this topic, please create a new topic for any further queries.