Transferring from Mac to PC. I manually moved Profile, got all my emails. But not Calendar. I've exported from it, got an .HTML file(??) Stymied now. Help!

I'm moving from Mac to PC. (Tip for young players: don't do this for fun). Have Thunderbird on both. I've successfully got my emails - by following the 'Manually moving files' instructions in https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer. However, it didn't move my Calendar data. I'm guessing that's coz Lightning is an Add-On. I tried exporting Calendar data on the Mac - produced an HTML file, (which surprised me, but hey what do I know?). My idea was to copy it to a USB, plug that into the PC, then Import it. However, there doesn't seem to be an Import function to do this (?). Can anybody tell me what I need to do to get my Calendar data over from the Mac to the PC please?