How to Perform Redundancy Switchover on BIG-IP

This really depends on what you are attempting to do. If your objective is to just failover from the active to the standby and allow it to take over should a failure occur on the new active then you can just do a "Force to Standby" and that will cause a failover event. If your intent is to failover and keep it in that state no matter what then you would do a "Force to Offline" which should make it so that F5 device never comes back into rotation until you mark it online again. In instances where you have both units as active unintentionally or in a failover loop you can also use "Force to Offline" to resolve that issue.