Final answer:
Iago wants Cassio to seek Desdemona's assistance in regaining Othello's trust as part of his scheme to make Othello jealous. Iago manipulates Cassio into believing that Desdemona can persuade Othello to reinstate Cassio, which sets up situations for Iago to suggest an affair between Cassio and Desdemona.
Step-by-step explanation:
In Othello, Iago wants Cassio to ask Desdemona for help in restoring Othello's faith in him because it is part of Iago's malicious plan to cause Othello to doubt Desdemona's fidelity. Iago believes that if Cassio speaks to Desdemona, it will provide an opportunity for Iago to suggest that Cassio and Desdemona are having an affair. He tells Cassio that Desdemona's goodwill is powerful enough to persuade Othello to be reconciled to Cassio. Confident in her own integrity and her persuasive skills, Desdemona agrees to help Cassio. This becomes a pivotal part of Iago's scheme, as it creates a situation where Othello can be manipulated into thinking his wife is unfaithful.