You can find the solution in the walkthrough (CTRL+F for "Cow-rustling" if you can't find the right section):https://docs.google.com/document/d/16XOUX_KXz800cLQ7VledpazkEZjviWRPpXzR3iswfmE/...
The walkthrough is linked in the game folder, and it's basically 99% complete. If you do find something missing, though, don't hesitate to ask me!