It will need to be filled and then painted using an artists brush trying to match the grain. It will never be perfect but you can get it to the point where someone else will never notice the repair unless you point it out. I would try to find a filler that matches the color of the dark grain and then buy artists paint
that comes close to the light grain. You or someone else is going to have to be an experienced paint
artist to do this right.
Just using filler will leave a solid color patch which will be very obvious.
The scratch I see can be taken care of by rubbing some diluted varnish
into it with a rag. The scratch will never go away completely but it will look better.