The Fine Tune button allows you to make small changes to an expense, regardless of what they have been paid or not. Things that can be changed by Fine Tune are;
Tax Code and Tax amount
To make a change, search for the relevant Expense by changing the date at the top of the Expenses screen.
Single-click the Expense and click Fine Tune on the right
When using Fine Tune, you can change any of the parameters presented in the Fine Tune dialogue.
Note that before clicking Save, a comment will appear beside that field advising the original value of a field;
Click Save to commit any changes.