To Add a Main Task

In the Customize dialog ( File > Settings > Configuration > Customize ) on the Tools tab, expand the Main Tasks tab.
Expand the User Tasks section.
Expand the open DGN library.
Do one of the following:

Select the open DGN library and click the New Task icon.

or
Right-click the open DGN library and select New Task from the pop-up menu.

or
Click and drag a custom toolbox from the left pane to the open DGN file.

A new Main task appears with the name "New Task", except when a toolbox is dragged from the left pane, in which case the new Main task has the same name as the toolbox.
Right-click the Main task, select Rename from the pop-up menu, and type a new name.
Click and drag tools from a DGN library or from the Application Tools in the left pane to the Main task on the Main Tasks tab.