reselect the pool member

Yes, this is in the pool configuration and is called Action on Service Down ad can be set to Reselect to select a different pool member. You can also use iRules LB::reselect to perform a reselect under specific circumstances if you want to.

Try this:

when LB_FAILED {
   if { [active_members [LB::server pool]] > 0 } {
      LB::reselect [LB::server pool]
   }
}