You can do this by right-clicking on the game in your steam library, selecting “properties,” selecting “local files,” and then selecting “Verify integrity of game files…”
If that doesn’t work, see the next bullet point to learn how to verify the integrity of your game files. Re-launch Brawlhalla and make sure you select yes when prompted by Steam to make changes to your hard drive.
If you are having an issue with Easy Anti-Cheat, read the following: