Screen Reader Text

There are multiple filters available in the plugin you can use. If you want the same text for each button, I would try something like this:

add_filter( 'scriptlesssocialsharing_buttons', 'rgc_modify_button_labels' );
/**
 * Modify the button labels on output. Applies only if the labels are set to
 * not show visually.
 *
 * @param  array $buttons
 * @return array
 */
function rgc_modify_button_labels( $buttons ) {
	if ( is_admin() ) {
		return $buttons;
	}
	$style = scriptlesssocialsharing_get_setting( 'button_style' );
	if ( 0 !== $style ) {
		return $buttons;
	}
	foreach ( $buttons as &$button ) {
		$button['label'] = 'Share on ' . $button['label'];
	}

	return $buttons;
}

This modifies the button label for icon only buttons (since the entire label output is wrapped in a screen reader friendly span). There are other ways you could tackle this, depending on how you would want to modify the output, but this seems the easiest to me. HTH