Should look like this:
begin
InfoFile := TStringList.Create;
Name := edtName.text;
Surname := edtSurname.Text;
ID := (edtID.Text);
PhoneNumber :=(edtPhone.Text);
try
InfoFile.LoadFromFile('C:\Users\grassman\Desktop\infofile.txt');
InfoFile.Add('NAME: '+Name);
InfoFile.Add('SURNAME: '+Surname);
InfoFile.Add('ID NUMBER: '+ ID);
InfoFile.Add('PHONE NUMBER: '+(PhoneNumber));
InfoFile.Add('Time of registration: ' + TimeToStr(time));
InfoFile.Add('Date of registration: ' + DateToStr(date));
InfoFile.Add(''); // Spacers to separate next set of details
InfoFile.Add('');
InfoFile.SaveToFile('C:\Users\grassman\Desktop\infofile.txt');
finally
InfoFile.Free;