Same way you get suntour cassettes off, ot not as I've been finding out today.
Tried the in the bike method, but getting very worried my new chain is stretching and snapping..
Tried off the bike and hammering at the teeth hard, still not managed to get it to twist.
Tried putting a bit of chain around the 11 tooth (creates flat edges for a spanner) and well my adjustable spanner is a few mm to small to lartch on.
I'm going the detaching the freehub route, for the same as shimano but you go in with a long 10mm Allen key for the other side. Of course my allen key is not quite long enough.
Got not a lot to do with this but hey just spent a good bit of time trying.
But shimano 6 speed was 3.65mm (according to sutherland 6th edition), with indexing that may just screw it up a little