Hi there. If you found your way here, it might be because you noticed that this quest as well as "Hardening the Hide" appear as non completed on your leatherworker. I took the time to make another one and found out quickly enough how i somehow missed those quests and will try to explain to you the best i can.
First of all, after you do a couple of quests in Dalaran, you're sent to see 2 NPCs: Celea in Azsuna and Hrul Sharphoof in Highmountain. Those 2 NPCs give you 2 quests each that can be done as long as you've completed the previous quests. And this is where you, me and a lot of people made a "mistake".
If you do those first quests at lvl 104 or higher, those 2 NPCs will immediatly give you the next couple of quests since you do meet the level requierement and naturally, most people would take and complete them, thinking those are parts of the quest chain, making the two quests we seek impossible to do anymore.
Both "Hardening the hide" and "Getting the kinks out" are meant to send you back to Azsuna/Highmountain once you hit lvl 104 AND have already done the initial quests.
To conclude, it is very easy to miss those 2 quests even back when Legion came out. And this is even more true today with heirloom gear.
I shall edit this post and see if party synchronisation can help us correcting this "mistake".
EDIT: so i had a friend helping me. He was lvl 120 but had no profession at all, he did learn LW, grouped me then party synch'd. It allowed me to do the initial quests until i finally reached the 2 quests needed.