Passing struct from main.cpp to a class
It looks like you're trying to implement polymorphism without implementing polymorphism.

What you have done is create three completely independent structures and assumed that they will all work together just because they are the same size, with similar names, and fields named the same. That's not the case. They are all completely separate.

Instead you want just one structure but to use it multiple times to create different variables:

// from ODriveArduino.h, but move *outside* the class
struct motor_Params{
      int axis;
      float vel_Gain;
      float pos_Gain;
      float vel_Int_Gain;
};

// in your code
struct motor_Params left_params = { 
    1, 2.5f/10000.0f, 40.0f, 0.0f/10000.0f
};

struct motor_Params right_params = {
    0, 2.75f/10000.0f, 40.0f, 0.0f/10000.0f
};

// later
  odrive.SetParam(left_params);