We have an array with dictionaries connected via plist, we also have a CollectionView which shows all the plist dictionaries and the ViewController (VC) by which we go through the CollectionView (by cells in VC). The question is how to select the desired dictionary to change the value of one of the dictionary values in the cell of which we passed.
Ps At this stage, we open the entire array and change the entire array (all dictionaries) boolean from false to True, then save and go to the specific cell to change the dictionary to which the particular cell belongs. It seems to have clearly stated his question, if not clearly write.
UPD Means enumerates all dictionaries The If condition fulfills with the required index, + the value changes to true (I see in the console) remains behind the small entry in this Dictionary 
This is what Console gives out (set BreackPoint in front of Write (WriteToFile))


