Take a look at the original sentence again:
No foot powder, no shoe insert, no expensive soap can kill the odor of Bartholomew's
feet, when he takes off his shoes, even
the goldfish gag.
You wanted to fix it this way:
No foot powder, no shoe insert, no expensive soap can kill the odor of Bartholomew's
feet when he takes off his shoes, even the
goldfish gag.
To delete the comma between feet and when would cause an equally bad problem, a fused sentence. A fused sentence occurs when you have two complete sentences joined with no punctuation whatsoever. No foot powder, no shoe insert, no expensive soap can kill the odor of Bartholomew's feet is the first sentence. When he takes off his shoes, even the goldfish gag is the second sentence. The spot between feet and when needs a stronger break than blank space.
You might want to consult the rules for fixing comma splices and fused sentences.
Go back to the sentence to try again.