Глобальная переменная

if (check==1)
{Form1->Edit1->Text = StringGrid1->Cells[ACol][ARow]; }
    else if (check==2)
    {Form1->Edit2->Text = StringGrid1->Cells[ACol][ARow];  }
Form2->Close();

#include "Unit1.h"

#include "Unit2.h"

class TForm1 : public TForm
{
__published:    // IDE-managed Components
        TButton *Button1;
        TEdit *Edit1;
        TButton *Button2;
        TEdit *Edit2;
        void __fastcall Button1Click(TObject *Sender);
private:    // User declarations
public:     // User declarations
       TEdit *Edt; //<<== Вот эту
        __fastcall TForm1(TComponent* Owner);
};

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  if(((TButton *)Sender)->Tag == 1) Edt = Edit1; else Edt = Edit2;
  Form2->ShowModal();
}

#include "Unit2.h"

#include "Unit1.h"

void __fastcall TForm2::StringGrid1SelectCell(TObject *Sender, int ACol,
      int ARow, bool &CanSelect)
{
  Form1->Edt->Text = StringGrid1->Cells[ACol][ARow];
  Close();
}

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    Form2->Show();
    Edit1->SetFocus();
}
 
void __fastcall TForm1::Button2Click(TObject *Sender)
{
    Form2->Show();
    Edit2->SetFocus();
}

void __fastcall TForm2::StringGrid1SelectCell(TObject *Sender, int ACol, int ARow,
          bool &CanSelect)
{
    ((TEdit*)Form1->ActiveControl)->Text = StringGrid1->Cells[ACol][ARow];
    Close();
}