This depends on which project type you are using. For netlist projects you use a combination of the Parts property and the pin number to set the auto-increment. If you are using the integrated project type then there is no need to define the pin numbers on the symbol, they are applied from the part mapping in the library.
There are examples of both mechanisms in the starter libraries delivered with the software.
The syntax for multipl pin numbers is a comma-separated list: 1,2,3 etc.