If it has already hit you, it can be difficult to make it go away. You normally just have to wait it out and hope that you start to feel better soon. There are quite a few things you can do to prevent motion sickness from happening in the first place. Click the link there for a full list.
The short list, if you don't want to read the full article is to try and replicate what is going on in game, with your body. So if your character is standing in game, stand too. If they are running, run on the spot. Drink water, use a fan. Check to see if the game has any options to help prevent motion sickness, some VR games do add support for stuff to help people out.