The HttpWatch installer normally installs the Chrome and Edge extensions from their official browser stores. On a PC without internet access, you can manually install the bundled, unmodified package that matches the browser by following these steps:

1. Locate HttpWatchForChrome.crx or HttpWatchForEdge.crx in the HttpWatch installation folder. The default folder is %LocalAppData%\HttpWatch for a current user installation or C:\Program Files (x86)\HttpWatch for an all users installation on 64-bit Windows. A custom installation directory may be different. A browser's CRX file is present only if support for that browser was selected during Setup.
2. In Chrome, open the extensions page.
3. Turn on Developer Mode.
4. Drag the bundled HttpWatchForChrome.crx file onto the extensions page and confirm that you want to add the HttpWatch extension. Do not use this procedure for a modified, locally packed or other third-party CRX file.
5. Turn off Developer Mode.
6. To install in Edge, repeat these steps on the Edge extensions page using the bundled HttpWatchForEdge.crx file.

More information is available in this blog post:

https://blog.httpwatch.com/2017/11/15/installing-a-chrome-extension-without-an-internet-connection/