How do you get partner in Yu-Gi-Oh GX tagforce?

It depends on which one you are talking about. Tag force 1 your partner is the person who your relationshiop with is strongest. Tag force 2 is whoever you choose which is the same with number 3.

In tagforce 1 find the partner which his relashionship is strongest. In tagforce 2 and 3 you get to choose your partner yourself