Function not returning sqlconnection

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C#

I made a function to get dynamic sql connection string,
but its not returning value when I am calling this function

What I have tried:

Function Decleration

public string GetConnectionString()
   {
       //return "Data Source=DELL\\HRMS; " +
       //    " Integrated Security=true;" +
       //    "Initial Catalog=CL1COM0032;";

       Common cmn = new Common();
       SqlConnection connn = new SqlConnection();
       connn = cmn.getConnectionForCompany(uInfo.prDBName);
       connn.Open();
       return connn.ToString();
   }

Function Calling

string connectionString = GetConnectionString();