Nut upsuser - Jun 2017 - procedure of recover FSD

hi:
    my nut server has redundant power and connect to different ups.
when one of the ups lost power, the nut server set the ups to "FSD"
correctly, so server connect to the ups can shutdown normally. but nut
server itself won't shutdown since it has another power source.

   now the ups get power again and the "FSD" flag should be recovered.
but it seems no procedure of the FSD recovery?

   thanks for help!!