Hi cecillemaquito,
We don’t have any settings for the transition/ animation to the gallery. You can view this javascript. go to theme folder -> library -> js -> attitude-custom-fancybox-script.js
Before making changes on the code first of all create a child theme. So that while updating to new version your customized code will not be lost. If you make direct changes on the code then each and every time while updating to new version same customisation should be made.
Thank you!