You will have to use a blender, grinding produces nut flour, not nut butter. You normally start from whole nuts, but now you have some preground ones, they should work too.
Be aware that most blenders don't have the power to produce nut butters. If you have a high-powered blender, it is still a hassle, because it is too thick. You have to use enough nuts to have a good flow (at least 500 g in a 2 liter jug), add oil, and use the tamper to get the nuts to move towards the blades. The more oil you add, the easier to do it, but your final product gets runnier. Almond oil would be ideal taste-wise, but a normal neutral oil will be good enough.
You can also add water instead of oil, to make the mix flow easier. You still can't add enough water for it to flow on its own, or you will end up with something more liquid than a paste. The taste is also much different than when adding oil. You can also add both oil and water.
When I got my Omniblend, this video helped me understand the process. However, my own results were never as thin as what she gets there. I don't know if this is because I bought preshelled nuts (which are drier), but I added water to compensate for this, and also used quite a bit of oil.
I don't know how commercial nut butters are made, but I suspect that maybe it is not a blade system, it could be that very fresh nuts are mashed between flat surfaces. That, or there is some blade system which, unlike a home blender, contains something to "feed" the nuts to the blades instead of relying on the blade sucking in the pureed mass.