Use the Rotate tool. Move the cursor near point P, and SketchUp’s inference engine should automagically “attach” to the exact end-point. By default, the rotation will occur in the plane of one of the adjacent faces. Depending on how you slightly move the cursor position, you can induce SketchUp to use either of the two adjacent faces (if they are not co-planar). If you want the rotation to occur about one of the principle axes, you can temporarily lock the rotation to Blue (press Up), Green (press Left), Red (press Right), or perpendicular or parallel to existing geometry (press Down once or twice).
Then click a second time on point A. Then click a third time along the guideline. You might need to draw a temporary edge along the guideline that spans the approximate region where point A is to end up. I don’t recall if that temporary edge is helpful to get SketchUp’s inference engine to jump the final rotation point A onto the edge,