Adjusting rear shock preload on Ninja250

Hi everyone, I tried adjusting my rear shock preload today but the collar wouldn't move a tiny bit.
Another problem is that the adjusting tool can't grip on the notch tightly and slips whenever I push harder.
I've tried doing it on the ground and on the rear stand but it doesn't seem to make any difference.
Any tips on doing this?
Thanks

Hammer

I don't think there's enough room to fit a hammer between the shocks and the wheel...but I'll give it try. Thanks.
Anyone else have another tip?

Screw driver/ pry bar on the notch then hammer it left or rite.
Note you will scratch it up, this is not the preferred way to do this but it works.