F5 Software Update for DNS Device

Hello Dear F5 Community,

i would like to ask you few question that i cant understand on F5 article.

i will upgrade one of my customer VE devices from 15.1.2.1 to 16.1.0, they are using DNS module.

and i prepare all the settings f5 recommend such as ; taking archive from both devices, re-activate their license, install the proper software,  verify the md5 with .iso but i saw and article regarding bigip dns software update.

here is the link for those who wonders: https://support.f5.com/csp/article/K11661449

my question is about Update the big3d process on all BIG-IP devices part on this doc.

as you know if bigip software is 15.1.2.1 then big3d agent is automaticly using the 15.1.2.1 version.

what will happen when i upgrade my standby device to 16.1.0 is big3d automaticly comes with 16.1.0 version.

so both device will not be same version big3d.

but document says big3d install command.

when will i update big3d. will i update big3d on my 15.1.2.1 not upgraded active device after i fnish standby upgrade process? or what will happen when i turn on DNS > Settings > GSLB > General. 

1. Select the Synchronize check box.

before both devices are not using same version of big3d?

any help regarding this guys?

Regards.