First thing I would do is get the engineering lead on a call to understand what changed and why they need the extra time. Once I have the details, I would put together a clear summary of the situation and escalate to my manager and the program stakeholders so everyone understands the risk to the launch date. I would make sure to communicate the impact transparently and set up a follow-up meeting so leadership can decide how they want to proceed. My job at that point is to keep everyone informed and make sure nothing falls through the cracks while the decision gets made.
My first move is a working session with the engineering lead within the hour — not to gather information for a report, but to diagnose the critical path. Is every one of those ten weeks truly blocking the launch, or is it two specific features? In my experience, about half of these slips come down to one or two resolvable blockers. I map the minimum viable scope needed to honour the committed customer date, identify what can ship in a fast-follow, and stress-test whether the blocking dependency can be parallelised with additional resourcing. Then I go to leadership with three options — full descope and launch on time, partial launch with a firm fast-follow date, or a negotiated slip with a compressed timeline and accountability owners. I own the recommendation. I do not walk in with a problem. I walk in with a path.