It might be easier to rewire your house! Is there a dryer plug close by?
From the diagram and pictures, 3 and 4 are connected together. To go to 120v. 1, 3 and 5 are connected together as are 2, 4 and 6. I don’t know whether or not the switch affects this.
in any case for 120v, 1 pole of the switch should be switching the hot line. The other two poles will swap how the start winding is connected.
With 240v both lines are hot and ideally they both should be switched but I think it would take a 4 pole switch to do that.
Is there any further info in the manual?