Champion/Challenger A/B testing will only work with trigger campaigns and engagement programs. You cannot use this with batch campaigns. https://community.marketo.com/MarketoArticle?id=kA050000000LGT0CAO
I thought once you have set the 1 champion and challenger it will send you an email prompt to tell you which is the champion and send out the email with the winning subject title.
If that is not the case than you can actually do it manually too.
Could you please provide me with the updated link to this? That link is no longer valid. Thanks!