what is the correct Rollback procedure of f5 HA upgrade

Hi Team ,

If we are upgrading HA pair , and say we have completed the upgrade on both the devices from version 15 to 16 and after some time application team reports an issue and we have to rollback the changes on both the device then what will be the step by step procedure .

We have to start the rollback from which device first ?

-Rollback standby device BIGIP-2 (version 16 to 15 )

-Failover from Active device BIGIP-1 (v16) to standby device BIGIP-2 ( v15)

-Rollback BIGIP-1 ( version 16 to 15 )