Moving this reply that was on a similar thread that you posted on, as you may find it helpful as well:
Glarbex
said
:
You need to use the ankou agitator on an ankou
before
you are in combat with it. If you use it on an ankou that you are already fighting (or which is fighting you) then you will get "Nothing interesting happens".
If done correctly, you will see the ankou say "AAACK". (I can't remember if this shows up in the chat box - it may only show in the actual game world display.)
You need to repeat this with quite a lot of ankous (though not a ridiculous number), and most of the time the "AAACK" is the only message you get. But eventually you will see "You feel your ankou agitator shake slightly..." and then a couple more messages as you make more progress.
I recommend to double check the ground to pick up the residue. Maybe you missed it or bad RNG? It is pink like this --> https://runescape.wiki/w/Ankou_residue
Are you using it on the correct ones? According to her when she gave it to you, you need to use it on a level 70 and above ankou. Those are the ones you can't typically attack as you get the warning this is not your ankou.
Now it is possible for the sub 70 ankou to drop it on a rare drop and a lootbeam does show when it does. I was fighting ankou training necromancy when I hit level 70 and got it as a drop and went what is this... Then got another like 6 drops and was like I can only have 1 what is this thing for. Then went might as well go make my t70 gear, and when they requested that item went oh well that was easy I guess.
When the day becomes the night and the sky becomes the sea, when the clock strikes heavy and there’s no time for tea; and in our darkest hour, before my final rhyme, she will come back home to Wonderland and turn back the hands of time.
1. Use the Ankou Agitator on a normal Ankou (level 61) in the Stronghold of Security (Level 4)
2. A level 72 Ankou will spawn next to it with ~30,000 HP
3. Kill a level 72 Ankou using Necromancy and it will drop 'Ankou residue'
4. Talk to Kili
5. Kili will take the Ankou agitator, the residue, and the garden pie from you.
6. DONE — enjoy your level 60 upgrades <3
(Make sure you don't already have Ankou residue in your bank from killing Ankou in the past)