Judging from [this question][1], there are no rules for training animals, so right off the bat you are entering homebrew territory.

If your DM is willing, then maybe you could train rats to help you. You can use spells such as Beast Bond and Speak With Animals to try and communicate with it. Talk to it, bribe it, and train it using these spells (Animal Friendship may not help much, other than to try and persuade it, which won't work unless you are speaking with it). 

DISCLAIMER: Rats INT score is 2. training it may become very difficult.

All in all, it is up to your DM whether or not you can do this.


  [1]: https://rpg.stackexchange.com/questions/59291/what-are-the-rules-for-owning-and-training-animals