I'm no master scripter, I'm quite stupid when it comes to it, but I want to know how or if I can get a script to go back to an original command, for example, I'm trying to make  a robot mine, then only put it in the storage until its full, but I want him to go right back to mining if there is no more of that material left, how do I make him go back to the starting command, because he gets stuck when there is no more of said material, I'm tired, so if something I said doesn't make sense, I can try to elaborate.

EDIT: Is there even a way to say "If X isn't here, skip X and (restart, move on to next step, go back to Y)"