You have to add the following piece of code into your Child’s Theme file “functions.php” and update the file.

/**
 * Filter password reset request email's body.
 *
 * @param string $message
 * @param string $key
 * @param string $user_login
 * @return string
 */
function wpdocs_retrieve_password_message( $message, $key, $user_login ) {
	$site_name  = wp_specialchars_decode( get_option( 'blogname' ), ENT_QUOTES );
	$reset_link = network_site_url( "wp-login.php?action=rp&key=$key&login=" . rawurlencode( $user_login ), 'login' );

	// Create new message
	$message = __( 'Someone has requested a password reset for the following account:' . $user_login, 'text_domain' ) . "\n";
	$message .= sprintf( __( 'Site Name: %s' ), network_home_url( '/' ) ) . "\n";
	$message .= sprintf( __( 'Username: %s', 'text_domain' ), $user_login ) . "\n";
	$message .= __( 'If this was a mistake, just ignore this email and nothing will happen.', 'text_domain' ) . "\n";
	$message .= __( 'To reset your password, visit the following address:', 'text_domain' ) . "\n";
	$message .= $reset_link . "\n";

	return $message;
}

add_filter( 'retrieve_password_message', 'wpdocs_retrieve_password_message', 20, 3 );