Other contributors have said "What can you do to help endangered whales?" is the same question as "How do you help endangered killer whales?". If you believe that these are not asking the same thing and should be answered differently, click here.
There are all kinds of groups around the world. The first one that comes to me is Green Peace. They try to help endangered spices all over the world. Perhaps you can type in Search Green Peace and contact them to see what it is that you can do to help.
Killer whales (ORCA) are not endangered at the moment. There are thriving pods everywhere.
Note: There are many species of threatened whales species, but the killer whale is not among them. The killer whale, which really is not a whale but a large dolphin, is still a fairly common species, and is rarely hunted. Please check the IUCN Redlist for endangered whales.