Single byte memtest errors — possible to tell which RAM chip is defective?
Not from that utility.  You’d need to see how the chips were laid out and what the addressing scheme was.  Since Apple doesn’t provide this, you’d be guessing.

Since these chips are soldered, they can’t be (user) replaced unless you take it to a shop that does SMT rework.  

Keep in mind it could also be the memory “controller” that handles the addressing of the memory that’s has also failed.  Usually when this work is done, all chips are replaced.