Core Data, Relationship - store multiple selected rows to entity

I need help - I want to store multiple selected rows from a tableView into one entity via relationship)
Lets say I have this: CoreData-Model: Entity_1 = Bags Entity_2 = Items
The user can create "Bagmanymaby bags for the hole family) and "Items" he want to put into a selectet Bag. So If the family goes on holiday every familymember has its own bag with some items in it. Some items will be in every "Bag" (if the user select them.)

Bags (for):
- Carol 
- Bens 
- Eva

Items:
- toothbrush
- towel
- shoes
- hairbrush
- makeup

--> I know the way to only store one item into each entity (via relationship). But I need helpt to store several items at once in the selected "Bag"
Ben only want to pick up: toothbrush and a towel Carol pick up all the 5 items Eva chooses toothbrush, makeup and shoes
If I open the tableViewController all the items are listed: I this I have to store all selected items into an array and then store the array to coredata. Who can give me a piece of code? Thank you for helping me.
FetchesResultsController:

    lazy var fetchedResultsCtrl: NSFetchedResultsController<Item> = {
        let request: NSFetchRequest<Item> = Item.fetchRequest()
        let sort = NSSortDescriptor(key: "itemName", ascending: true)
        //let catSort = NSSortDescriptor(key: "kategorie", ascending: true)
        request.sortDescriptors = [sort]
        let fetchedCtrl = NSFetchedResultsController(fetchRequest: request, 
managedObjectContext: self.managedContext, sectionNameKeyPath: nil, cacheName: nil)
        // an UserDefaults binden o.ä.:
        //NSFetchedResultsController.deleteCache(withName: "kategorieCache")

        fetchedCtrl.delegate = self
        return fetchedCtrl
    }()

TableView:

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) ->
 UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: reuseIdentifier, for:
 indexPath) as! detailsInterieur
        let items = fetchedResultsCtrl.object(at: indexPath)
        cell.nameLabel?.text = items.itemName

        if let paths = tableView.indexPathsForSelectedRows {
            if (paths.contains(indexPath)){
                cell.accessoryType = .checkmark
            }
            else {
                cell.accessoryType = .none
            }
        }
        else{
            cell.accessoryType = .none
        }
        cell.selectionStyle = .none

        return cell
    }


override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
         print("select")
}


override func tableView(_ tableView: UITableView, didDeselectRowAt indexPath: IndexPath) {
         print("deselect")
}

EDIT: I can find the selection with this code:

guard let selectedRows = tableView.indexPathsForSelectedRows else {
            return
        }

This functions are generated automatically. But how can I use them in the right way?

@objc(addBag_RELObject:)
@NSManaged public func addToBag_REL(_ value: MyBag)

@objc(removeBag_RELObject:)
@NSManaged public func removeFromBag_REL(_ value: MyBag)

@objc(addBag_REL:)
@NSManaged public func addToBag_REL(_ values: NSSet)

@objc(removeBag_REL:)
@NSManaged public func removeFromBag_REL(_ values: NSSet)


@objc(addItem_RELObject:)
@NSManaged public func addToItem_REL(_ value: Item)

@objc(removeItem_RELObject:)
@NSManaged public func removeFromItem_REL(_ value: Item)

@objc(addItem_REL:)
@NSManaged public func addToItem_REL(_ values: NSSet)

@objc(removeitem_REL:)
@NSManaged public func removeFromitem_REL(_ values: NSSet)

from Core Data, Relationship - store multiple selected rows to entity