Make sure you have the Oculus software installed. Follow the link here.
libovravatar.dll is installed in this directory C:\Program Files\Oculus\Support\oculus-runtime\
Steps for using the CrossPlatform sample scene can be found in the Readme in it…
Please check that you have selected ASTC in the Build Settings > Texture Compression dropdown. If your Unity console has an exception mentioning ASTC, this will likely fix your issue.