Increasing Item quantity in Cart of repeated list items

Hello Everyone,

I’m having a hard time trying to do something like incrementing the quantity in the cart item. As far now I am a beginner in Appgyver and coding side, Its bit difficult for me to figure out. Take a look at the app screen shot bellow,

Its a repeated item list from my device data resources with list of items in it like {itemName, itemPrice, itemDesc and itemQty}. I can bring the item and its schema to cart when I click on the items from the item list page to cart page.

But from the cart I need to increase or decrease the item quantity by pressing the plus or minus button. Bus as per my knowledge I reached until this, with formula
IF(pageVars.addedQty >=1, data.mapItemsResult[0].vQty + 1, 1)

But when I tap the pluss button it increase the value on all the item in my cart not specifically on the tapped item.

Also I need to sum the total amount on bottom by multiplying the quantity of each repeated item.

Hope you get my point, and reach me back soon.

Mine is a simple cart:-

I have used Sum() function for each and every appVariable( i.e item)

Assigned value formula in my case for “+” is:- Sum([appVars.item1 , 1 ])