APA 6th: adding a comma when 2 different citations of 3 or more authors


I did quite a bit of research, but did not find any answer to this. Using APA style, if there are 2 different citations of 3 or more authors with the same year shorten to the same form (e.g., Johnson, John, Black, Smith, & White, 2008 and Johnson, John, Black, & Purple, 2008 would both be shorten to Johnson et al., 2008), we need to cite as many authors as needed to distinguish the citations, and add a comma and et al. (as in Johnson, John, Black, Smith, et al., 2008). However, Endnote won`t add the comma. Is there a way to fix this? Thanks!

the comma<space> need to be inserted infront of the et al in the author list setting of the citations.  I assume you already found the Ambiguous Citations setting there?  see the attached image.