1) Download your OpenPlugin from Marketplace Plugin Inventory:
https://marketplace.reallusion.com/inventory-list?plugin=1

2) Make sure to download the proper version. (v8.00 for iClone 8, v7.93 for iClone 7)

3) Unzip the file and copy the entire folder.
(Note: Sometimes an extra folder would be created automatically by your zip software, just make sure to copy the main plugin folder)

4) Right-click on the iClone icon > Properties > click on [Open file location].
Go into OpenPlugin folder
(The default file location should be: C:\Program Files\Reallusion\iClone 8\Bin64\OpenPlugin)

5) Paste the plugin folder.

6) Launch iClone, the plugin will be in Plugin menu > Python Samples

===Install plugin manually===

Here is another way to install plugin if iClone does not load the plugin.

In Script menu > Load Python > Find the plugin folder and select [main.py] > Click [OK].
The plugin will be installed in Plugin menu.

More info: https://youtu.be/K9fKrBxczhA?feature=shared