Hi,
it is best practice to use "using" to create,show and destroy the modal forms. you should check for whether user is changed something and clicked accept button (which a button sets DialogResult = DialogResult.OK).if he click "cancel" button (which a button sets DialogResult = DialogResult.Cancel), you should not do update cell value. have attached sample.
ViewAgenciesByJobsForm.ShowDialog(this)
sets current form as parent form.