Oops

More like "ouch"!

Certainly will have a stadium full of raised hands when asking if this ever happened to anyone else.

Can't really tell from the picture, but is that a chip missing or just crushed wood?

Whenever I get crushed fibers from a ding, I'll try to place a wet rag over the spot and use a clothes iron or other appropriately sized heat source to steam out the dent.
The idea is that the water will swell the fibers and (mostly) restore the original shape.

Depending on the position, I'd probably wad up a wet rag, set it on a plate and prop up the object with that corner buried in the rag to soak up the water for a few hours.

Then comes the heat, probably a heat gun in this situation. Just heat and repeat until things look better!

If this is a box, I'd also consider just cutting off the top x" amount to get past the ding if the water didn't work.

splint has the 2 best answers and just looking at that one picture I'm not too sure which way will satisfy.  
However, my first instinct would be to put a 3/4" straight router bit in the router table and "take off" as much as needed to get to 'good wood'  and allow another walnut border to be glued in place.  I see you already have a walnut trim, you can accessorize with a second walnut strip and call it design.  I would make it bigger in height and width than needed and either rip off the excess on the TS or router table then finish sand to meet the host wood.
Probably doesn't make too much sense, but think about it a while, it will then.

btw - some of my neatest designs come from exactly what you have

Instructor I once knew called these situations "Design Opportunities".

My solution has been to glue on patches.

What’s the item?
Can you simply cut all 4 corners back and call it your design?
The picture suggests the miter may have opened behind the ouch. If so, you’ve got a bigger issue if it needs to be structural.

Maybe bevel all the edges to match?

Wow, thanks for all the suggestions!  I ended up using a dado blade to make a new that removed the crushed corner. I will fill the rabbet with more walnut and it the original plan.  Might even look better.  

I'd definitely go with the Splinter solution works beautifully if you are patient. Just a matter of time. Once the wood swells up you can also apply a wet rag and a hot clothes iron. Soak and iron, soak and iron. 

If all that did  not work and you have more of the same wood, Try cutting out the damaged pieced leaving a real flat area  and then cut some pieces to match and glue them in. I have done this numerous times with good luck. Look over the board to find a very similar grain pattern and be sure to match the grain direction!

I was gonna say just drop it on the other 3 corners but it sounds like you got it sorted out 😉

Dropping it entered my mine, but then I thought better of it. 

Yeah, but then you'd probably drop it onto your toes...

I like the ding the other 3 corners approach. 

BTW, the wet rag and iron method works well for dents in flat surfaces but you have to be careful using heat on a glue joint.  PVA wood glue will melt and the joint will be ruined if it gets too hot.  I use a heat gun to un-glue joints and remove PVA glue from bad repair jobs.  It doesn't take much heat to make the glue fail.  Heat and moisture will loosen hide glue joints too but you can reclamp the joint and the glue will readhere.  

That’s a nasty dent. How high is your bench? What type of wood is that? 
There are a lot of good ideas here. I would get some Timber Mate and slowly build it up sand and stain or paint it if all else fails. Good luck I wish I could see the rest of the box.