First check you have the following Arnold core : >22.214.171.124
(tested on 3dsMax 2022).
Then simply set the ARNOLD_PLUGIN_PATH environment variable to rtoa/bin path.
In Windows 10/11 click the win button and start typing 'env' you should get an hint like 'Edit the system environment variables', clicking on that it will open 'System Properties' .. at the bottom you'll find the 'Environment Variables'. You can then add the ARNOLD_PLUGIN_PATH user variable (or system variable) pointing to the rtoa/bin folder.
If the dll is not found you need to install Intel2019 redistributables (Intel64.msi) :
Here romboReflectFlakes with a MapToMaterial.
To properly load Rto3dsmax demo scenes add their texture paths to AssetTracking -> ConfigureProjectPaths.