A servitor is when rather than working directly for your end you invest energy in creating an entity that will do the work for you. A servitor can be a one shot creation that does one thing and then is gone or a persistent spirit that can be built up and assigned tasks. Long running servitor workings often require “fed” in some manner (food, money, sexual energy, electricity…)
A servitor is a kind of thought form, so it can work in most any manner you can imagine from being rather robotic to having its own powers of reason and some amount of free will.
As for advice when you don’t have practical control… First if there is anything at all that you can do to help bring about the result you desire then you should be doing it. The sigil working should make it easier for you to focus on doing what you need to do if it is effective. If there really isn’t anything you can do, then the sigil should at least capture your desire so that it can move to unconscious fulfillment. You should find yourself less frequently thinking about your desire after casting your working, particularly if it involves worry, that should diminish. When casting a curse, success is foremost indicated by a reduction in feelings of anger.
Combining these thoughts with a servitor… when launching a servitor you may more or less split off the part of you that is desiring the end so that it can work independently and unconsciously. Or, tell that part of you that it’s okay, the servitor is going to take care of things and it can chill while the servitor does the work.