A successful chess-playing computer would prove either that a machine can think or that chess does not involve thinking.
Conclusion
If a successful chess-playing computer were invented, the conception of human intelligence would certainly change.
Evidence
If a successful chess-playing computer were invented, it would either prove that a machine can think or that chess doesn't involve thinking.
Evaluate
This argument is saying,
This implies that both B and C would each lead to Z.
How does that match up with the actual concepts from the argument? The successful chess computer will lead to "a machine can think" or "chess doesn't involve thinking". And the author thinks either one leads to a change in the conception of human intelligence.
Formally:
if we thought a → change conception of machine can think human intelligence
if we thought chess → change conception of didn't involve thinking human intelligence
Goal
The author assumes that currently we think "machines can't think" / "chess does involve thinking" (otherwise learning either of those things couldn't possibly change us).
But the author is also assuming a weird connection between whether machines think / whether chess involves thinking and how we think about human intelligence.
Since the author never discussed "our concept of human intelligence" in the evidence but is talking about it in the conclusion, we can expect our answer to have language referring to "our conception of human intelligence".