The table average stats are added using Layout Manager in the same way you add 'normal' player stats. They are listed at the bottom of the Stats dropdown.
Ah, this is the PAHud section of the forum - please keep PT3 questions in the PT3 section.
To enable table averages you must create a new Group and set it to 'table averages: show on table'. See the HUD Guides in theDocumentation and the How To: HUD Configuration for information.
Average pot size is not yet available, but you can add other table average stats.