It’s good that you have another reason to resubscribe, so that should all work out. Note that there are two levels of “download” here:
You can just download the notebook file itself by doing “File → Download (as notebook)” from the running notebook. That just gives you the “ipynb” file. If you actually want to run the notebooks locally or in some other environment, that is a much more complicated question. For starters, you have to download the whole tree of files associated with each assignment. Here’s a thread about how to use tar to do that. Then you have to get the appropriate versions of all the required packages installed and configured. We don’t have official instructions for how to do that, but here’s a thread to get you started.
The one other high level point to make is that there is no way to download all the assignments of a given course in one shot. You have to deal with each of them individually, although there are a few cases in which both the assignments in a given week are in the same file tree.