It looks like a screw in type. Make your own spanner type wrench with a couple of 1/4 inch bolts and a 1 x 2 piece of wood about 12 to 15 inches long. Position the bolts so they go thru the wood and match the spaces at the perimeter of the flange....then just use it to undo the flange.
"If it can't be reduced, reused, repaired, rebuilt, refurbished, refinished, resold, recycled or composted
then it should be restricted, redesigned or removed from production."