Just use a rag or cotton ball moistened (wet, but not quite dripping) with some WD-40. Wipe down the strop to remove the heavily 'caked on' excess compound. The good thing about the WD-40 is it'll thin the compound a bit, which will allow it to be distributed more evenly, in a very THIN layer. Let the strop dry a while (you can use a hair dryer to speed up the drying). What you should have left is a strop in the natural color of your leather (perhaps darkened a bit by the WD-40), with a slight greenish cast to it. After the leather is completely dry, chances are it'll perform better as a strop than it did with all that excess compound. You should be able to strop without collecting & scraping green stuff off of the strop.
Edited to add:
I've made 3 or 4 strops using the green compound. In every case, I've always gone back and treated them as described above. It's very easy to initially put too much compound on. The very nice thing is, after treating my strops this way, once dried they perform even better than they ever did. I think the WD-40, after drying, leaves the leather just a little bit dryer than it was originally and, therefore, a bit stiffer. Combined with the thinner, more even layer of compound, that makes it work a lot better.