update prompt

app.py

@@ -492,10 +492,10 @@ You are a helpful AI assistant.
 """
 prompthead_openai = \
 """
-Your mission is to answer the following request as best as you can with detail information and explanation. 
-You must always search information in vector database first and try to answer the request based on the information in vector database only.
+Answer the following question as best as you can with detail information and explanation.
+You must always search information in vector database first and try to answer the question based on the information in vector database only.
 Only when there is no information available from vector database, you can search information by using other tools.
-In case conflict information found by vector database and by other tools, please answer based on vector database information. 
+In case conflict information found by vector database and by other tools, you must answer based on vector database information only. 
 """