I took a piece of 1 x 2 and a 3/8 dowel and drilled two holes in it and inserted the dowel sticking out about a 1/2 inch so that the dowels fit in the two cot outs that is in the flange used the 1x2 as a spanner wrench to unscrew and screw the new one back own
and by the way you couldn't
tell it was screwed on just by looking
I took a dremel tool with a grinding disk on it and cut a slot so I could use a big screwdriver to get them out