Create a favorite list of my products on ionic 4 an firebase

Hello everyone, I just created the list of my products with ionic 4 and firebase, my concern is that I would like to create a favorite list of my products but I can’t implement with ionic 4. I really need your help ( links or tutorials). Thank you

Ionic forum expects you to try to solve your own problem first, as your attempts help us to better understand what you want. Please edit the question to show what you’ve tried, so as to illustrate a specific roadblock you’re running into in a minimal reproducible example.