Change prediction of finished game and recalculate scores and ranking

You can use the audit log to identify the users that changed their predictions, and also determine their last ‘legal’ save. With that information you can write some update queries for your database. Just make sure you make a backup before running a query. Once the database is updated you can do a new calculation. That will fix the ranking. An example of one such query is*:

UPDATE pool_wp_predictions SET
  home_score = 0, 
  away_score = 0, 
  has_joker = 0 
WHERE match_id = 21 AND user_id = 1;

*) change the table name if you have a different table prefix

You can find the match_id in the audit log. User ID can be found in the dropdown, or on the pool user admin page.

Another option is to delete this one game. And then do a calculation. In that case all players will be affected, but this by far the easiest solution.