Select: BuildingSplit Room The cursor appears as a crosshair. The information line shows: [Click Left] at wall=Position split point and start dividing wall
Click at the split point in the first wall. The cursor drags a polyline. The information line shows: [Click Left] in room=Corner of dividing wall [Click Left] at wall=Finish dividing wall
Define the wall up to the split point in the second wall.
Click at the split point of the second wall. The room is split. The operation is finished.