Who had the handkerchief at the end of act 3 and why in he book ohello?

At the end of Act 3 in Shakespeare's Othello, the handkerchief is in Bianca's possession. She is a courtesan who receives it from Cassio. The handkerchief is significant because it was a gift from Othello to Desdemona and serves as a key plot point in the play as Iago uses it to manipulate Othello's emotions.