ANA initiated a 'Bid My Price' program for upgrades. 7 days prior to departure, you may receive an email allowing you to bid for PY. Not sure if a UA booking on NH-operated would be eligible.
https://www.ana.co.jp/en/us/servicei...rnational/bmp/
You won't be able to redeem miles for a PY upgrade until after 9/2019, as NH PY is offered as a separate class of booking or complimentary to NH elites.
https://www.ana.co.jp/en/jp/amc/news/info/201810/py/
Based on load and to squeeze extra revenue before conducting op-ups, ANA will sell upgrades at check-in. These can be as low as $500 for Y to C. You should inquire upon check-in, but this is not published and happens on a case-by-case basis.