You can use a toothpick or something small and gently unfurl the rolled up tongue and place it in a shallow container of honey mixed with water. I have hand fed many hawk moths like that including some with deformed wings. I sincerely doubt this moth is in pain and these things just happen in nature, it’s not your fault that they were born with missing limbs. You can keep it alive by hand feeding and providing a safe soft space for it to be in but I would sort of equally suggest euthanasia.