what to do-DS156 andDS157 incorrectly filled

One of my friend applied B1/B2 but he didn't fill the form correctly.

In DS156:
36. Has anyone ever filed an immigrant visa petition on your behalf?
He said YES. Actually it should be NO.

DS157:
10. List allcountries that have ever issuedyou a passport.
USA,Thiland, Europe ...
My stupid friend actually visited above places only. He didn't fill
the form correctly due to language barriers.

He has already received interview appointment which is scheduled in a
month. Is it better for him to wait for the interview chance to
explain, or better to send a letter first?

Thank you.

Fred

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