re-ordering tabs

The link to the WooCommerce doc is the authoritative guidance on reordering tabs so its worth persevering.
– in what way didn’t it work? ie had no affect, gave you a white out or an error message?
– try increasing the priority parameter from 98 to PHP_INT_MAX
– ensure you are using straight quotes ' " and not smart quotes ‘ ”
– ensure the first line of functions.php contains: <?php
– in wp-config.php, set define('WP_DEBUG', true); and see if any errors or warnings show up
– validate the whole contents of functions.php using this service:
http://phpcodechecker.com/
– your code should go in functions.php for a child theme to make it update-safe
– paste your functions.php at pastebin.com (free service) and post the link here so others can take a look

The error that you give is what you get if you set a tab property for a tab that does not exist for the particular product. To avoid this, enclose every tab= line with an isset() check, so:

if( isset($tabs['more_offers']) ) {
  $tabs['more_offers']['priority'] = 5;   
}