OTBI: Succession plans report, how can I add the Incumbent person number?

Hi all, I have a problem in editing a report on succession plans. I have these columns (Plan ID, Incumbent name, Candidate name, Person number).

I want to add a column with the Incumbent's "person number", but when i try to do that the person number is not that of the incumbent, it is that of the candidate. I don't understand how to force the person number columns to read the candidate person number or the incumbent person number as appropriate.

Many thanks in advance.