Way to Retrieve Lost Quest Items

Is there a way to retrieve lost quest items? I tossed out the Mark of the Three as I thought it was a spare Blood of the Watcher. Obviously this has deadlocked me progress through FG as I can’t get passed the portal beyond Kymon.

Thanks

If you’ve threw away a quest item, I think it should be re-obtainable after restarting the character, and if it is not, you would need to use a program that allows you to add items whenever you please. For example GDStash.

You can always recover critical quest items from the quest givers.