Update app.py

app.py

@@ -26,7 +26,7 @@ def concat_tool(arg1:str, arg2:str)-> str: #it's import to specify the return ty
         arg1: the first argument given by user
         arg2: the second argument given by user
     """
-    result = "arg1" + "arg2"
+    result = arg1 + " " + arg2
     return result
 
 @tool