There may be an issue with the mechanism.
No matter which way I turn it or how much I turn the screws, I get no movement.
But thank you all for your replies!
That is a possibility. if someone turned it all the way counter clockwise far enough the screw will come out of the nut or housing. I don't recall which set up the Valkyrie has. In either case you will need to remove the chrome ring and put the screw back in the correct position.