on the spanner wrench you are using, is the hook at the end rounded or is the end mushroomed out? If it is, then you need a new spanner wrench. If not then proceed as follows;
If you look at the preload collar on the shock, there is what looks like little windows in the collar above the preload ramps. with the hook of the spanner wrench in a window on the backside of the collar turn the wrench clockwise or counterclockwise (depends which way you faced the curve of the spanner wrench. With the curve of the spanner wrench against the preload collar radius, you will be turning the wrench with the hook at the end/rear of the direction so the hook is 'pulling' the window not pushing the window). If the collar is hard to turn, spray/drip some light oil (Kroil oil, 3 in 1 oil, etc., etc.) so that gravity pulls the oil between the collar and the shock body to help if there is rust or corrosion.