Hi,
What you're gonna want to do, if you haven't already, is back up your original game files
so you have something to fall back on in the event that something goes horribly wrong.

To replace the model, all you have to do is go to the following directory and replace the 'giganotosaurus' file there with the 'giganotosaurus' file contained in this ZIP file:
C:\Program Files (x86)\Steam\steamapps\common\Jurassic World Evolution\Win64\ovldata\Content0\Dinosaurs

To replace the genome library images the same rules apply, but with the files called 'Dinosaurs_SizeLarge_Giganotosaurus' and 'DinosaursSizeStandard':
C:\Program Files (x86)\Steam\steamapps\common\Jurassic World Evolution\Win64\ovldata\Content0\UI\Icons