number of steppers in ListView when i change the quantity i want to increase the amount

Hi,
I'm making a very simple app with Xamarin forms where I've products with a quantity for each one. Everything is saved in a database:
From a ListView it has a Stepper to increment this quantity, but pressing on it, nothing change from my amount,because i am unable to get the productid,how can i get the id using mvvm
My XAML

http://prntscr.com/hgodet