Hello. You need to unzip the archive to the RustEdit>CustomPrefabs folder, open your map in RustEdit and go to Prefabs>Prefabs>Custom. Find the arena prefab there and drag it to the place on the map where you want to add it, the options window will open and you need to apply all the modifiers there. When applying the height modifier, you may need to do some corrections to the objects around it. Save the map and run it on the server. For the arena to work, you need to install oxide and the Oxide.Ext.RustEdit.dll extension