Hey, this should partially provide answers: https://steamcommunity.yuanyoumao.com/workshop/filedetails/discussion/1693186543/1678063648154786059/

In the example Flatlands is used, the ID for Medium Flatlands is 1710378799

Search for "animal" you will find those lines for the animals:
<action type="SetAnimalPopulation" animal_types="wolf" min="15" max="20" era_factors ="1 1 1 1 1 1"/>

adjust min & max, the era_factors are for less or more animals in specific eras.

In Medium Flatlands those values are usually decimals seperated by a dot .
like 0.8 or 0.25

To remove extinction for certain animals modify the value to 1 for each era (6x 1 ):
era_factors ="1 1 1 1 1 1"

Hope this helps. Feel free to join the community discord or ask more detailed questions here. https://discord.gg/WbsHwWT