How to Use an Update Statement in SQLDataAdapter

I am trying to run an update statement after i built my sqldataadapter. I have column called INIT_PHASE in my table and if the INIT_PHASE is null or there is no data then i would like to set it to 1. I have tried but i can't seem to get it right the update statement. Pls. help. here is my code:

 string ID = ddlPractice.SelectedValue;
    string TYPE = DDL_TYPE.SelectedValue;
    SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["myConnection"].ConnectionString);
    SqlDataAdapter da = new SqlDataAdapter(@"select SET_SK, UNIT_NM, TYPE, INIT_PHASE FROM myTable WHERE UNIT_NM =@ID AND TYPE = @TYPE", con);
    DataTable dtSETS = new DataTable();
    da.SelectCommand.Parameters.AddWithValue("@ID", (ID));
    da.SelectCommand.Parameters.AddWithValue("@TYPE", (TYPE));
    da.Fill(dtSETS);

    if (dtSETS.Rows.Count > 0)
    {
        DataRow dtSETS_row = dtSETS.Rows[0];

        long SET_SK = dtSETS_row.Field<long>("SET_SK");

        if (dtSETS_row.Field<string>("INIT_PHASE") == null)
        { 

           //run update command here

             update myTable set INIT_PHASE = 1;

        }
    }