Part

Part 1:
Expand Solution-Explorer > TwinCAT Project > SYSTEM > TcCom Objects
Right-click on Object (XtsProcessingUnit) to open the context menu
Click Add New Item... in the context menu
Part 2:

The Insert TcCOM Object dialog box opens.

Expand Beckhoff Automation GmbH > XTS Modules
Select XtsPart [Module]
Enter the number of parts required in the input field Multiple
Double click on the selection or confirm with OK

One or more parts are added to the Processing Unit.