Controlling form components from another form in C#

Forms should NEVER know about other forms, nor the controls on them. Doing so ties them together so the code/form cannot be reused elsewhere.

Your second form needs to expose its own events that another form can subscribe to. These events would signal what's happening on the form and it's up to the subscribing form to determine how to respond to those events.

Forms should only be concerned with their own controls, not with the controls on other forms.

I managed to control the textboxes by adding this code to The First Form

public partial class Main : Form
   {
       private static Main frm;
       static void frm_FormClosed(object sender,FormClosedEventArgs e)
       {
           frm = null;
       }
       public static Main getMainForm
       {
           get
           {
               if(frm==null)
               {
                   frm = new Main();
                   frm.FormClosed += new FormClosedEventHandler(frm_FormClosed);

               }
               return frm;
           }
       }

and by double clicking the datagridview in the the second form

private void dataGridView1_DoubleClick(object sender, EventArgs e)
       {

           Main.getMainForm.bSave.Enabled = true;
           Main.getMainForm.bSave.Enabled = true;
           Main.getMainForm.tClient.Enabled = true;
           Main.getMainForm.tType.Enabled = true;
           Main.getMainForm.tFirst.Enabled = true;
           Main.getMainForm.tSecond.Enabled = true;
           Main.getMainForm.tDriver.Enabled = true;
           Main.getMainForm.tCity.Enabled = true;
           Main.getMainForm.tNumber.Enabled = true;
           Main.getMainForm.tPrice.Enabled = true;

           this.Close();

       }