changing the entries on one column based on another column

I'm a bit of an Excel newbie, so I apologize if this is covered a lot. I have some survey results, imported into Excel in csv format. In one column, I have the results to the question "What is your diagnosis?" with numerical answers (it's multiple choice). In the next column, I have the results of the question "How confident are you of your diagnosis," also with numerical results (scale of 1-10).

Some respondents answered "I don't know" (9) as the diagnosis, and then answered "Very confident" (10) as their confidence level. While it is correct to say that one is very confident that one does not know the answer, for the purposes of this survey, this needs to be recoded as low confidence that they do know the answer. Thus, I want to change all of the entries in the second column to low confidence (1) if the respondent answered "I don't know" in the diagnosis column.

So, is there a command or function that says "If the entry in column A == 9, then make corresponding entrty in column B=1. Otherwise leave it alone. "

Thanks!

billo