I searched through the faq, and didn't find the info I am looking for. Sorry if this is a rookie question ...

I have an upcoming trip booked on NZ (SFO-LAX-AKL-ADL out, MEL-AKL-SFO back), and the initial SFO-LAX flight is a code share with United (UA operated). I cannot do the seating assignment on this leg through NZ; is there some way I can do that through United? I am a 1K, so would like to get access to E+, or even an exit row (even if it is just a short flight).

Thanks!