issue with dropdown

app.py

@@ -23,8 +23,8 @@ def set_model(model_name_str):
     global tts
     tts = TTS(model_path)
     speakers = tts.get_speakers()
-    value = speakers[0] if speakers else None
-    return speakers, value
+    speaker_dropdown.choices = speakers
+    speaker_dropdown.value = speakers[0] if speakers else None
 
 def main():
     logging.basicConfig(level=logging.INFO)
@@ -65,8 +65,7 @@ def main():
         debug=True
     )
 
-    model_name_dropdown.set_action(set_model)
-    model_name_dropdown.set_action(set_model)
+    model_name_dropdown.observe(set_model, "value")
 
     iface.launch()