So putting together the @Interitus384 and @Animacio.org strings you get - thanks all this one was a real bear
I:\UE_5.1\Engine\Binaries\Win64\UnrealEditor.exe “F:/UE4/Towny 5.1/Towny.uproject” -run=DataLayerToAssetCommandlet “OpenWorld.umap” -DestinationFolder=“/Game/DataLayers/