Installed extension doesn't show up

Find a puzzle icon on the right side of already visible installed extensions (near ...). Click on it and a drop down of installed extensions is now displayed. Click on selected empty pins and it should work.

Image from this Google support questions

1. Enter chrome://flags/ into your address bar
2. Change Enable Enhanced Bookmarks to disabled
3. Click Relaunch Chrome button at the bottom

You should now be able to install the extension again

If you're sure that the extension doesn't show up in Settings>Extensions:

The default location for all Chrome extensions is

C:\Users\<username>\AppData\Local\Google\Chrome\User Data\Default\Extensions

When you navigate there, you'll find that all the folder names are cryptic, so you'll have to isolate the particular extension either by Date Modified, or by clicking in each folder and comparing the version number to the version number of the extension (find via the extension's page on Chrome Store).

To remove the extension just delete the particular folder, and restart Chrome.