You will need to replace the counter with a single piece of stone. Look at it as a great chance to give a refreshed look to the room.

I think Cooks Kitchen advice is good. However, if for now you have to try to make it work the rounded edge could be sawed off and then you'd seam the sawn edge to the back of the lower piece. The seam will likely be more conspicuous than normal.

I would bet that would cost more than buying an all new basic stone counter.

My issue is that all of the counters match so changing it would require changing all of them. Also, I’m not sure if I described it correctly. It’s designed like this picture.

Tried to add a picture, not sure if it worked..

If you want to reuse the granite then lower the backside to a comfortable level but not straight across.

or

to get straight acrosswith no seam then a new countertop is needed

or lower it with a seam

If it's a smaller island, maybe you can find a remenant which is a left over piece from countertop fabricators.

Plenty of kitchens have a contrasting stone on the island. Do that.

This bar top was lowered and not by me. The guy imbedded a metal rod and it still doesn't look too bad. It depends on the movement and particulates in the stone as to how well it turns out or not. I'm certain I could get to inconspicuous and acceptable, but as cheap as replacement stone is, it may be tough to be cost effective.

The rounded edges can be ripped off on site. It certainly isn't a ridiculous idea.

I found a picture of the lowered top with the rod in the upper right corner.

It is possible to choose another stone for the island if you post pics of the perimeter counter we could maybe suggest a different island counter .

howd it turn out? thinking of doing the same but adding metal to the seam to make it a design piece

I want to lower my bar height counter as well. Will a contrast stone look good if it’s attached to the original counter stone? If done right, would the seam be to obvious or look bad? I have a couple of seams in my counter Bc it’s very long. They don’t look bad. Hardly noticeable.