To define the return type of an operation you have to specify:
The return type for the Java method: in the General tab of the operation property sheet. If the return value in Java is a Java class or an array of Java class, PowerDesigner will generate an output message type based on the return class structure
The output message type for WSDL: for simple return value, the output message type for WSDL can be defined in the Web Method tab of the operation property sheet
For more complex return types, you can manually define the output message schema using the SOAP Output tab of the operation property sheet.