Installing pet makeovers is different from standard CC because they are "household" files, not just individual mods:
This guide explains how to install and use the custom (featuring a shy dog named "Dachsie") created by Blue Ancolia for The Sims 4 . Prerequisites Dachshund dog makeover at Blue Ancolia
In the advanced filters on the left, check the box for "Include Custom Content" . Installing pet makeovers is different from standard CC