This is not hard. Tell the actor it's his job. The design has changed and the staging of the scene needs to change. It's actually not about the actor; it's about the play. And it's about the audience. Take the note.

It’s never easy being a director. Trying to hold everything together at the same time. Like a seamstress with seams threatening to burst at any point with pressure coming from everywhere. Neither is it, for the actor, trying to stay true to the imaginary circumstance and deliver lines, react and at all times, be aware of their fellow actors and their own safety. And facing new circumstances that come their way. But communication is key. Why the change, is it necessary and if it is, how can both director and actor accept the change and how can things improve because of it. Explain, communicate, create together and not dictate. Perhaps that would be a step forward.