1)
To enable the system standby manual boot, use the system standby manual-boot command. To disable the system standby manual-boot option, use the no form of this command.
system standby manual-boot
system no standby manual-boot
2)
To switch over to the standby supervisor, use the system switchover command.
system switchover
So for your question you need to do system switchover to failover from active sup to standby.
HTH
regards
Inayath
**Please do not forget to rate the post if helpfull******