If you want to return any money to the owner you have currently held on their account, the first step is to add a payment to the owner using the funds held.
Note: Make sure to tick the box Use funds held on account.

This will create the entry in the statement as shown below.

The next step is to select the created payment entry in the statement and then do a payment run.
This will clear the held on account amount from the statement.

The last step is to go to Agency > Add/edit owner > section Payment details > sub-section Commission settings and change the setting for Minimum owner account value: to £0.00.
Scroll to the bottom of the page and click Save,