If it's like the other MKH's the pin is all you need to remove, and the chassis will "just" slide out backwards from the tube, like this:
View attachment 122385
Obviously that's not working for you, so a couple of possibilities:
- There's a felt ring at the capsule end, to keep the chassis centred in the tube, which could have got itself stuck to the tube.
- The tube might be dented or slightly bent, and it's pinching the chassis which stops it moving.
Once the pin is removed the chassis should rotate in the tube, so you may be able to loosen it by twisting before trying to pull. (Maybe plug a sacrificial XLR in, so you can grip it with pliers without damaging the mic itself?)