On iOS, you can rate items by tapping or sliding the stars on item images, on the item details or via long press. Rating is an important part of training your Hai as well. You can always re-rate your your items after you rated them. Find all your recent ratings in your Profile.
In your Discovery Feed
In Item Details
[Secret Gesture for iOS] - Hard/Long Press an item!
Tap and slide the stars, or swipe left for a 2 star rating or swipe right for a 4 star rating