Hi Ronald,
If there is only issue in accessing the management controller(mc),we can restart mc B from cli of controller A.
#restart mc B
If you would like to reboot the storage controller (SC)B.This will cause temporary loss of data availability
#restart sc B
For more info please check page 147 https://support.hpe.com/hpesc/public/docDisplay?docId=emr_na-c03791989
Thanks
Sahana R