how to maintain user credentails changes through app.config file for database after install exefile

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C#

hello every body,

I have a doubt, how to allow user changes on config file for database accesing in user system.

For example: I am mainting database with my credentails in my system.
then after instalation how to user login with his cretentails? how is it posible?

I developed my project using c# and sqlserver 2005. I maintain my database with my credentials, but when it is installed in client machine the environment is diferent. So what is the way to maintain the user credentails?

for example my crystal report is working based on my credentails in my system but how to allow user in his system to call reports based on his credentails?

plz give any sugestions on this and give any examples to maintain user status.