For installing this Plugin:
1. Save the zipped(!) folder somewhere on your computer.
2. Open QGIS, go to Plugins > Manage and Install Plugins > Install from ZIP.
3. Click on the 3 dots, browse to the zipped folder and then click on Install Plugin.

The plugin ("Create Rockyfor3D Input Rasters") is available from the plugin menu, the processing toolbox or directly from the toolbar.
