How to assign a Fallback Persistence?

If you have no experience then it might be easier for you to just assign a fall-back persistence from the GUI.

FWIW in tmsh the fallback is fallback-persistence

You'd set the persistence with something like

modify vs_name fallback-persistence fb-persist-profile

and create (Before you add it obviously) the persistence profile via something like

create /ltm persistence source-addr profile-name

The type (Where I have source-addr) can be one of the supported types. e.g. cookie, src/dst-addr etc.