Your way is outdate for tmx
Files. There is no TiledAtlas anymore. In case you use an older version just use the regular TmxMapLoader
without packing your grafics.
Here is a simple example how to load a Tilemap:
TmxMapLoader load = new TmxMapLoader();
TiledMap map = load.load("path/to/file");
You can even combine it with an Assetmanager:
assetmanager.setLoader(TiledMap.class, new TmxMapLoader(
new InternalFileHandleResolver()));
Please take a look to the answer i made at this question to get more information about the texture stuf where it need to be and how you can change the filepath inside of the .tmx and so on:
tmxmaploader-to-use-packed-tileset