Create a custom Gravity Forms merge tag

gforms-merge-tag.php

<?php
/**
	 * Add custom merge tag to the merge tags drop down in the form editor
	 *
	 * @param array $merge_tags
	 * @param int   $form_id
	 * @param array $fields
	 * @param int   $element_id
	 *
	 * @return array
	 */

add_filter( 'gform_custom_merge_tags', 'custom_merge_tags', 10, 4 );
function custom_merge_tags( $merge_tags, $form_id, $fields, $element_id ) {
	$merge_tags[] = array( 'label' => 'Custom Merge Tags', 'tag' => '{custom_merge_tags}' );
	return $merge_tags;
}

	/**
	 * Replace custom merge tags in field content if they are found
	 *
	 * @param string $text
	 * @param $form
	 * @param $entry
	 *
	 * @return string
	 */

add_filter( 'gform_replace_merge_tags', 'replace_merge_tags', 10, 3 );
function replace_merge_tags( $text, $form, $entry ) {
	$tag_merge = '{custom_merge_tags}';
	if ( strpos( $text, $tag_merge ) !== false ) {
		$text = str_replace( $tag_merge, 'Here it is!', $text );
	}
	return $text;
}