The easiest way to fasten / unfasten the nut that locks the tailstock I found is with a ratcheting spanner of the type sold e.g. here https://www.aliexpress.com/item/3290...archweb201603_
The important property here is that the ratchet is both flat and flexible, i.e. it will fit easily into a constrained space. And because the spanner is ratchet-operated, tightening or loosening a nut is quick.