The ability to edit any incorrectly saved Call Sessions sits under the main menu "Manage" >> Call Sessions.
Use the dropdown menu "Date Range" to help filter your past call sessions. In the right-hand column, you then have the option to "Delete" the session all together or "Edit" the session to correct any errors.
If you're editing the session use the cursor to click on the field that needs to be updated and add in the correct numbers. Make sure to "Save" to lodge the correct details.