Specific cell of UICollectionView

I'm a new swift developer and simply; I'm trying to update the third row of CollectionView cell based on the other two cells ( third row will have a label in which it have the result of substitution of first row label and second row label) but I didn't find a solution to handle such an idea.

This is a list of attributes to handle the two values

var total : Int = 0
var totalp : Int = 0

This is the cellForItem function

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as! CollectionViewCell

        if(indexPath.row == 0 ){
            getSumSales { (success) in
                if success{
                cell.price.text = String(self.total).convertedDigitsToLocale(Locale(identifier: "AR"))
                } else{
                //It is not updated and some error occurred. Do what you want.
                }
            }
        } else if (indexPath.row == 1){
            getSumPurchses { (success) in
                if success{
                cell.price.text = String(self.totalp).convertedDigitsToLocale(Locale(identifier: "AR"))
                    
                } else{
                //It is not updated and some error occurred. Do what you want.
                }
            }
        } else if (indexPath.row == 2){
            print(indexPath.count)
            cell.flag.isHidden = true
            var diffr=self.getDiff()
            if(diffr > 0){
                cell.price.textColor=UIColor.green
            } else {
                diffr *= -1
                cell.price.textColor=UIColor.red
            }
            print(String(diffr))
            cell.price.text = String(diffr).convertedDigitsToLocale(Locale(identifier: "AR"))
        }
        
        cell.name.text=locationName[indexPath.row]
        cell.layer.borderWidth = 3
        cell.layer.borderColor = UIColor.clear.cgColor
        cell.layer.cornerRadius = 20
        return cell
    }

And this is the git difference function

func getDiff()-> Int{
        let diff = self.total-self.totalp
        return diff
    }