The spindle itself won't adjust.

The entire headstock assembly will need to be adjusted.
It's possibly done by the grubscrews (No. 48), but there will likely be some correct order to do the adjustment. Probably slacken the main mounting bolts, adjust the grub screws, then re-tighten. You may need to fully remove the headstock to work out how they adjust, but you'll have to be aware of any shims that might have been used.