The latest IRIS+ parameters are included with the latest mission planner software so its best to load them directly. I attached a screenshot showing how to load the parameter files for the IRIS
1 - The first step is to connect to your IRIS+
2 - Go to the Config/Tuning tab
3 - Go to the full parameter list
4 - On the right you will see a dropdown box with various APM vehicles, select the 3DR IRIS+ parameter
5 - Click on the load button to load the parameter fie, a new window will popup showing the parameters that will be updated, click on continue. Also make sure that all the parameter files are checked.
5 - Now to save these parameters to your IRIS+ click on the write button.
Hope that helps.