Drop the sink, toss the blocking, install a couple Sink Straps (GranQuartz), clean the sink flange and stone bottom, silicone, clamp the sink through the drain with a bar clamp and a 2x4, snug the Straps, check the reveal and adjust, tighten the straps, spray the silicone squeeze-out with Windex, spit on your finger, and wipe away the excesss.

Thanks, @Joseph Corlett, LLC. I think they will have to take the counter off & re-do it; the problem arose because they had the overflow facing the wrong direction and the sink won’t fit correctly in the cabinet when it’s turned around.

Most of the time, sink overflows are situated in the front wall of the sink, just as yours is. You don’t see it there unless you bend over and look.

3 baths, two have Kohler sinks with overflow at the back and one wide oval Kohler in the master with the overflow in front. 1955 bathrooms. Is there really a right or wrong direction - they all work.

Per manufacturer specs, the overflow on this sink goes in front, not in the back (under the faucet). But installation is unacceptable, regardless of overflow location.

Update: the company re-made the countertop. But then they broke the sink when attempting to remove it from the first countertop. :(