How do I add this extension to Inkscape?

https://inkscape.org/~mattia.basaglia/%E2%98%85tgslottie-importexport

Looks like apart from dropping the zip file into your Inkscape extensions folder, you also need to install an additional Python module.

How do I install the extra python extension?

This is more python related than Inkscape:

********************************************
This involves using an Adminstrator Command Prompt
You can quite easily damage your Windows installation
Or delete other users files - Use at your own risk
********************************************

From this page, https://www.activestate.com/resources/quick-reads/how-to-install-pip-on-windows/

In the windows search bar type 'cmd' then right click on the command prompt icon. Choose 'Run as Administrator'

cd C:\Program Files\Inkscape\bin

From the page above:

1. 

curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py

2. 

python get-pip.py

Then: 

pip.exe install lottie

I have attached a screenshot from my VM Window 10 terminal