Spokeshaves seldom come an owner’s manual. There are lots of good videos on YouTube worth looking over and most of them have some very good tips on tuning and improving them. Adjustment varies by spoke shave type. I found that you can set the blade in a common metal shave just shy of the sole, snug up the tightening screw enough to keep the blade in and (keeping the shave upright) LIGHTLY tap a handle on a bench and then checking the advance of the blade by attempting a light cut on a piece of scrap. By alternating handle taps you an advance each side separately. Likewise, you can back a blade up by turning the shave over and taping the handles as required. Some workers like to have one side of the shave take a heavy cut and the other take a light cut. If you are doing smaller items it allows you to vary the cut as you wish without having to reset the blade. I have found that shaves with adjustment knobs are not always consistent. Some seem to work well and some don’t. If they don’t then you can disengage (or remove) the knobs and use the tap method of adjustment, I have also used a small brass hammer to tap the back of the shave blade in, similar to adjusting wedged planes. Just remember to finish tightening the screw to keep everything where you want it.
Most wooden shaves without adjustment knobs are tapped in lightly with a small hammer, tapping the posts to advance the blade and the underside of the blade to back it up. If the posts are too loose to hold the blade where you want it then the shave needs some rework.