I started the Red Dragon takeover and killed all enemies, including the boss, except for one. I looked around and saw his red arrow inside of a building that I can't enter. I'm early in the game & I don't have incindiary weapons or the chemical launcher yet. How can I finish the mission?
I'm sorry to hear that you have experienced this issue.
As this is a control point and not a main mission I would recommend leaving the area and trying to start another control point or a side mission if possible, then after you have completed it return back to the Red Dragon control point. Hopefully this will reset and you will be able to complete it without encountering the issue again.
However if this is not the case and the issue persists could you please provide a video of the issue and confirm what you have tried.