Someone already posted console commands for this, but if you have issues every time you start the game, you can set the launch options on steam.

1. Find Wolfenstein ET in your library and right click on it
2. Select Properties
3. Under General tab, there is a box that says Lunch Options Launch Options
4. Paste this in the box: 5. Optional: Change any settings you want (like resolution)
6. Done!

Edit: bon appétit