How to select something within an XML attribute?

I am currently attempting to replace a certain string in an xml document. I am doing this through Visual Studio using C#. The exact string I want to replace is Data Source = some-host to Data Source = local-host. The string is located under an attribute to my Strings. However, the attribute connectionString has many values under it.

<Strings> <add name="Cimbrian.Data.ConnectionString" connectionString="Data Source=some-host;Integrated Security=false;pooling=true;Min Pool Size=5;Max Pool Size=400;Connection Timeout=5;"/>

I have managed to be able to select and replace the entire values for both name and connectionString however I want to be able to select JUST the Data Source = some-host to replace.

After loading the document my code currently looks like this,

XmlNode ConnectNode = Incident.SelectSingleNode("//Strings"); XmlNode add1 = ConnectNode.FirstChild; add1.Attributes[1].Value = "THIS REPLACES ALL OF CONNECTION STRING";

But as the string value suggests, it is replacing far more than I want it to. Any help would be appreciated. Apologies if that is slightly hard to follow.

EDIT - I forgot to mention that if possible I want to do this without searching for the specific string Data Source = some-host due to the fact that the some-host part may change, and I still want to be able to edit the value without having to change my code.