StoreMigration.swift

lazy var persistentContainer: NSPersistentContainer = {
    let container = NSPersistentContainer(name: "app container name")
    
    guard let fileContainer = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: "your group.app.identifier") else {
        fatalError("Shared file container could not be created.")
    }
    let groupStoreUrl = fileContainer.appendingPathComponent("app container name.sqlite")

    let hasOldStore = FileManager.default.fileExists(atPath: container.persistentStoreDescriptions.first?.url?.path ?? "")
    let needsMigration = hasOldStore && container.persistentStoreDescriptions.first?.url?.absoluteString != groupStoreUrl.absoluteString

    if !hasOldStore {
        let description = NSPersistentStoreDescription(url: groupStoreUrl)
        container.persistentStoreDescriptions = [description]
    }

    container.loadPersistentStores { (storeDescription, error) in
        guard error == nil else {
            print("Error loading persistent store", error!.localizedDescription)
            return
        }

        guard needsMigration else {
            print("Store migration not needed")
            return
        }

        guard let oldStoreUrl = storeDescription.url,
              let oldStore = container.persistentStoreCoordinator.persistentStore(for: oldStoreUrl) else {
            print("Cannot locate old store")
            return
        }

        do {
            try container.persistentStoreCoordinator.migratePersistentStore(oldStore, to: groupStoreUrl, options: nil, withType: NSSQLiteStoreType)

            var error: NSError?
            NSFileCoordinator().coordinate(writingItemAt: oldStoreUrl, options: .forDeleting, error: &error) { (urlForModifying) in
                do {
                    try FileManager.default.removeItem(at: urlForModifying)
                } catch let error {
                    print("Error deleting old store file", error.localizedDescription)
                }
            }

            if error != nil {
                print("Error coordinating deleting old store", error!.localizedDescription)
            }
        } catch let error {
            print("Error migrating store", error.localizedDescription)
        }
    }

    return container
}()

Migrate core data persistent store from app container to security application group identifier for use with app extensions and so on.