Hands is the best insecticide, after the initial gross you won't mind anymore except for the finger becoming green(or black, depends on the aphids
).
I had the same results with neem oil, not much instruction on how to use it online.
You must use a drop or two per liter and add some dish soap that should make some chemical reaction(probably help break it apart), not super effective however.
Another eco friendly way is to spray them with a strong water jet to remove them, they will return in a few days but after the leaves are bigger they won't eat it anymore or do less damage at least.
On a side note, a lot of aphids could also mean the plant is not happy.
My sister had a big kumquat tree in pot that had tons of aphids and mealy bugs, I was tired of seeing it in such a poor state that I decided to put it in the ground where it would have needed less cure(it was practically abandoned) and there was a lot of mold in the end of the pot, probably due to poor drainage. Never saw any parasite since then.