What buttons does the BPMN tab bar have?
Beside the general buttons, the BPMN tab bar provides the following buttons.

Change symbol: Changes the symbol of a selected object or the symbols of all selected objects of a type.

Add lane: Adds a new lane to a pool or lane.

Insert lane: Inserts a selected lane in the selected pool or lane.

Delete pool or lane: Deletes the selected pool or lane.

Move lane: Moves the selected lane in the required direction.

Transform into call conversation: Transforms communication elements into call conversations.

Change type of sequence flow: Specifies the type of a sequence flow.

Collapse subprocess: Collapses a subprocess object.

Expand subprocess: Expands a subprocess object.

Edit: Opens the assigned model contained in the subprocess on a separate tab for editing.

Select global reference: Opens the dialog Select global process or task to assign it to a Call activity.
See also
What are tab bars for?