Just replace it.
string dbsourcedbSource = "data source=myserver\sqlexpress";source=myserver\\sqlexpress";
dbsource
int sLen = dbsourcedbSource.IndexOf("=") + 1;
string getString = dbSource.Substring(sLen, dbSource.Length - sLen);
dbSource = dbSource.Replace("myserver\sqlexpres"getString, "whatyouwantotoreplaceitwith"whatyouwantotoreplaceitwith");