Application schema support is a GeoServer extension and is downloaded separately.
- Download the app-schema plugin zip file for the same version of GeoServer.
- Unzip the app-schema plugin zip file to obtain the jar files inside. Do not unzip the jar files.
- Place the jar files in the WEB-INF/lib directory of your GeoServer installation.
- Restart GeoServer to load the extension (although you might want to configure it first [see below]).