If you didn't allow the option of automatic sending of the best creation, you have to evaluate and decide on your own which creation wins and when it should be sent to the rest of the recipients.
1. Find your A/B test campaign on the campaign list in the main menu of the Mailing tab, click on the gear icon and then on AB Test Statistics.
2. Analyse the data on the displayed modal and decide which creation won the test.
3. To order the mailing of the selected creation, click the Send button.
Mailing to the rest of the group of recipients starts immediately.