'Unfasten' in the Bible

His announcement was, "There is One coming after me mightier than I--One whose sandal-strap I am unworthy to stoop down and unfasten.

saying to them, “Go into the village in front of you, and immediately as you enter it, you will find a [donkey’s] colt tied, which has never been ridden by anyone; untie it and bring it here.