Aperture ring lock on Sigma 70-300mm lens?

I have a Sigma 70-300mm lens for Nikon. It is giving me an error which generally means that one does not have the aperture ring locked. I would love to lock the ring but I can't figure out how to. Does anyone here have this lens and have advice on how to fix it?

Here is a link to the manual (thank you Gary Huston)

The aperture issue is listed on page 2:
<For Nikon AF/MF, Minolta MF>
When you use the program exposure mode or the Shutter speed priority auto mode, the Diaphragm control ring must be set to the smallest F-stop (i.e.largest number). All Nikon AF/MF lenses have a safety button which should be moved to the lock position (fig2).

And on page one, fig2 is shown an aperture ring and its lock button.

I have the Nikon version of this lens. "All Nikon AF/MF lenses have a safety button which should be moved to the lock position (fig2)." I can't find either the aperture ring or safety button. How is it possible I can't find this component of my lens? I should note that I had this problem a few years back, remember finding a switch, switching it and the problem was solved. I really wish I remember how I did that…

Super thanks to anyone who can solve this mystery.

Generally you turn the ring to the minimum aperture, usually f/22. At that point, you should be able to lock the ring. Some brand lenses with aperture rings however, may not have a lock, but as long as the aperture ring is always at the minimum aperture, the lens should work.

Fee? Just turn to largest f/number. IF there's no lock then just leave it there. If the error persists, take off the lens and clean the electrical contacts with a cotton bud on both sides, camera and lens. Electrical contacts only, not the glass.

If nothing seems to work, you have bumped into a lens that is not compatible with your camera. Not much you can do. That's the risk of buying third-party. Compatibility will not always be perfect.

Thank you all I understand exactly what you mean many thanks.