Do you have a seed and some mana potion in your stockpile? (as opposed to laying on the ground that is not a stockpile or being held by a pawn) If so, there should be a lot of surgery options in the health bill.

Read how it works.
You create the seed first. Make sure to keep it in the freezer as it's organic like meat.
Your shaman has to have enough mana. Don't remember how much it is at first, but when fully upgraded it takes 80 or 90 mana. If you have mana storage built, either remove the "Magic" work in the Work tab for your shaman, draft them to get more mana from the storage, or simply make them drink a mana potion.
Open the health tab of the patient and chose the necessary operation. Make sure your shaman is assigned to doctoring/surgery.
The shaman will do surgery automatically or you can force them to do so.

Having a similar problem - I have the seed, a couple of mana potions, and have medicines of all tiers available, and can add the appropriate surgery bill to regrow a body part. But I can't actually tell my druid to perform the operation: gives the "need material" warning.

edit: And of course, I try it the next day, and it DOES work. Welp.