"The first thing I would do in this scenario is deploy a method to get to the bottom of why we were behind as a team. I have used various root cause analysis methods, and I frequently lean on the 5 Whys method in cases such as these.
Once the cause of the delay was identified, I would work with my team to develop a strategy to address it. If there were performance issues, I would assign mentors and ask that they spend extra time leading those who need help. If a stakeholder or client was behind on their responsibilities, I would have a discussion with them about the impact of their actions and develop a way forward. These types of actions usually correct the issue and my teams get back on track quickly.
If the delay was something that was outside of my control, I would be transparent with my client or stakeholder. I would ensure them that the team would work to complete the most valuable pieces of the project on time and determine if there was an opportunity to remove anything unnecessary from scope. I would also offer any relevant updates to the delivery date as needed."