You could try one of these.
https://ebay.us/m/28EL6S
If not I think it's a case of cutting it off, I never like messing too much with wiper motors that go through glass I always have visions of it smashing.
Funnily enough, that's exactly what I ended up buying.
The bigger puller did get the arm off, but the arm broke it as it was so seized...new arm ordered and now fitted.
The smaller puller was then invaluable as I had to reposition the new arm a couple of times to get it into the correct place and it goes on rock solid each time!
