When a customer emphasizes "as soon as possible," the primary objective is early value realization, not necessarily a methodology change. The project manager should first assess opportunities to deliver value incrementally (A) by identifying which deliverables or features can be released earlier, how value can be decomposed into usable increments, and what dependencies constrain early delivery. This aligns with benefits realization and progressive elaboration: deliver the highest-value outcomes sooner, gather feedback, and adapt subsequent work. Jumping straight to detailed requirements refinement (B) may be helpful, but it can delay delivery if done exhaustively up front rather than focusing on just-enough detail for the earliest increment.
Creating a full-scope plan "using agile" (C) is premature before deciding whether incremental delivery is feasible within constraints (e.g., regulatory approvals, integration dependencies). Approving a change request to shift to agile (D) is not the first step; the PM must first evaluate delivery options and confirm what approach best supports early value given scope, risk, and organizational context. Incremental value assessment enables an informed delivery strategy and stakeholder alignment.