If they're cruising RIGHT NOW, then they should already know the correct protocols, and if they don't, it's a little late to be asking about them at this point.
It's essentially 'use it or lose it'. If you don't use all of it on a single excursion, you can use the remaining toward another one.
The excursion credit cannot be used for anything else, and you'll lose it if not used for an excursion.
We have ~$5.00 remaining after booking two different excursions on a 7-day cruise.
We have HIA for our March '23 NA 7-day sailing. DW and I were offered one dining credit each for Tamarind or PG (no Canaletto) for our complimentary specialty dining choices.
I see on HAL's site that Rudi's is only featured on Pinnacle Class (Koningsdam/NS/Rotterdam). Am I missing something here? Is it typically offered as a 'pop-up' on other ships, and if so, when do we know when it will be available for a particular sailing... only after boarding?
Which is exactly why I prefer to manage my own bookings directly with HAL every time. Eliminates the middle person, so they can't muck something up. If something gets mucked up with my bookings, it's on me, and I have no one else to blame.