Well, restart, or (re) activate?

if it is stuck in SMS mode, because the profile puts it there, you should probably power off the partition, and then power it on again, but override the profile setting to SMS mode.

to power on a partition:
chsysstate -r lpar -m $P520 -n $partitionname -f $profilename -o on -b normal

to restart a partition:
chsysstate -m $mSys -r lpar -o shutdown -n $partionName --immed --restart

or

chsysstate -m $mSys -r lpar -o shutdown --id $partition-D --immed --restart