First you will want to make sure to have already configured your Oculus using the software provided with the VR Visor.
To setup iRacing to use your Oculus, you will need to go to members.iracing.com and click on "Settings”.
Then you will need to run the graphics configuration tool by clicking on the "Launch” button.
This will open the "Auto-Configure Graphics” setup.Once you get this screen, click on the drop down menu button:
Then in the list, find and select the display you have previously configured for your Oculus:
The last step is to click the "Auto Configure” button:
Optionally, you may also use the graphics options in Sim to fine tune some visual settings.