To do this you must name the cell in Excel (as opposed to VBA).

On sheet "Form 6", select "Insert > Names > Define" and name the cell in the dialog.

In code you can do Sheets("Form 6").Range("D89").Name = "InstType" which sets the name on the sheet, or you can set a Range variable to the cell and use that instead. The main difference between the two is lifetime - the Range variable lasts as long as the code is running, the cell name sticks with the cell.