In the Speed and Consumption section in the voyage drawer you can update the various fields for consumption for a voyage. This section can be found in the Overview-tab in the voyage drawer.
When the drawer is opened you will find the section like this:
In order to expand the section to see and edit the fields, click the icon on the far right of the section.
Once the expand icon is clicked the fields will be displayed like this example:
Note that if the field for Speed Laden or Speed Ballast is changed in the vessel section it will also affect the corresponding field in this section as well, and vice versa.