Yes, you will need this resource pack and all you have to do is edit the formation link. I think you can add formations too but haven't actually gotten to that yet.

C:\SteamLibrary\steamapps\common\Age of Wonders Planetfall\Content\Title\Packs\Species_Humans

MewMew thank you for taking the time to answer my question,I really appreciate it :)
I need to ask a little guidance from you,I found the files and they are in .RPK
Now I'm not familiar with these kind of files,I tried to open it with several applications like Atom.Notepad and even good old Notepad,and I get these squarish strings and then some names with random numbers like this:
https://imgur.com/a/OO5GXvO
Could you please explain to me how can I increase the number of the units within this file and which numbers should I modify?
Let's say for example I want to increase the basic Vanguard Troopers from 3 to 5,any help will be much appreciated.

You need to open the files using the games modding tools, it's a option in the PDX launcher. In the package manager it opens you'll first need to create a new mod, after that under tools you can open the Resource Editor and open the .RPK.

Originally posted by Akazury:

You need to open the files using the games modding tools, it's a option in the PDX launcher. In the package manager it opens you'll first need to create a new mod, after that under tools you can open the Resource Editor and open the .RPK.

After a bit of searching within the options I could find the way to increase the squad size,thank you.