It's under the regular hotbar tab, "enable pet hotbar" I believe it is. I play on the PS4 but the options are the same as PC, having recently switched to PS4 from PC.

A better solution is to put your pet abilities on your cross hotbar. Enable the L2+R2 and R2+L2 combination. I have my Place set to R2+L2 Up on d-pad, Left is Heel, Down is Away, Right is my Chocobo. Triangle is Obey, X is Sic, Square is Teleport, and Circle is Steady (which I never use)