Yep, you'll probably have to back it off the top using your finger, or if you have it, the nylon-toothed "comb" which BMW issued back in the day, that is now rarely seen. I think there was a thread in which these were discussed... search function time if you want, but if you don't have it, no loss, The Man Upstairs gave us fingers to do this.
The good news (maybe) is that IF it's stuck at the top from running up there full blast and essentially coming to a hard stop and in this case the motor hasn't enough starting torque to get it going down. If you use a finger to back it off maybe only half an inch (less if you're lucky) it may be that the motor can do the rest.
Down the road, so to speak, you want to adjust the regulator so that it comes to a soft stop at the top. There is an adjustable bumper in the regulator mechanism for this. Lotsa luck...
You also want to get into the motor once you have it out, and clean any old hard grease, grime etc from it's little electrical guts, bearings, brushes and armature so that it doesn't have trouble starting next time, all by it's isolated lonesome. Bench test fully.
