You can install the RC with e.g.:

pip install astropy==4.1rc2

and test it with (make sure you have pytest-astropy installed, which you can do with pip install pytest-astropy):

python -c "import astropy; astropy.test(remote_data=True)"

This will produce a long sequence of dots and letters indicating the test is running. At the end you should see something like

=========== 8949 passed, 115 skipped, 73 xfailed, 1 xpassed, 2 pytest-warnings in 476.85 seconds ===========

If this shows no failures, you can report it in the table below as a "success", otherwise put it as a "failure" (and if need be you can create an issue in the astropy issue tracker).

Perhaps more importantly, you can also make sure that your package(s) work properly with this version of astropy (since this is not covered by the test suite).

If you are in a hurry and already have the astropy git source set up, you can also just checkout the v4.1rc1 tag. Don't forget to fetch the latest changes first (git fetch --all). Note, though, that installing with pip is preferred, because that's closer to what users will do.