How to programatically modify the connection string of a flat file-source component using SSIS in C#?

I have set a source destination mapping in SSIS. I am setting source to a flat file component(text file contents) read and mapped to Sql DB and insertion is being done accordingly. I want to change the flat file Source connection string alone dynamically and save to destination mapped. Set flat file Source connection string is not getting updated.

Mapped Source Path Connection String:
string strSourceConn = @"D:\SSIS\Test3\empdetails.txt";

Source path Connection String:

string strSourceConn = @"D:\SSIS\Test3\emp.txt";
// Create a new SSIS Package

//Package package;
Microsoft.SqlServer.Dts.Runtime.Application app;

string pkgLocation = @"D:\SSIS\Test3\Integration Services Project2\Integration Services Project2\Package.dtsx";

app = new Microsoft.SqlServer.Dts.Runtime.Application();
package = app.LoadPackage(pkgLocation, null);
// Add a Connection Manager to the Package, of type, FLATFILE
var connMgrFlatFile = package.Connections.Add("FLATFILE");

connMgrFlatFile.ConnectionString = strSourceConn;
connMgrFlatFile.Name = "My Import File Connection";
connMgrFlatFile.Description = "Flat File Connection";

package.Execute();