To Assign a Main Task to a Task

In the Customize dialog ( File > Settings > Configuration > Customize ) on the Tasks tab, expand the User Tasks section.
Expand the open DGN file.
Select the task to which you want to assign a Main task.
(Optional) In the Properties pane, right-click and select the Add Main Task property.
Click the arrow to the right of the Main Task Path property and select the Main task that you want to assign to this task.
When you select that task in the Tasks dialog, the Main task appears with it.