Question: how to download crx file manually?
Answer: Download the CRX file to your computer for the Chrome extension you want to install.
Go to chrome://extensions/ and check the box for Developer mode in the top right.
Use a CRX Extractor app -- I used CRX Extractor -- to unpack the CRX file and turn it into a ZIP file.
Locate the ZIP file on your computer and unzip it.