Python 3.9 is not even released for 10 days yet. As far as i see a lot of the packages are not supporting Python 3.9 yet. I think your best bet is to uninstall Python 3.9 and install Python 3.8.6.
If you want you could try the following just to make sure, but i think i won’t work.
pip intstall pipwin
pipwin install <package name>