Swift 3.0如何使用TableView单元格更改按钮标题

I have a table view with subclassed table view cells. I have attached a button and hooked this up to the table view cell's VC. I want the button to say 'Add' upon loading, 'Subtract' when clicked and back to 'Add' when clicked again. But I am having trouble understanding how I can relate the row number with the state of the button.I have a table view with subclassed table view