Sometimes, you may need to install a WordPress plugin that is not in the WordPress.org Plugin Directory. A typical example is when you want to install a premium theme that you have purchased and downloaded from a third party source.
Below are the guidelines for installing WordPress plugins by the upload method.
First, download the plugin you want to install from the source. The plugin will be in .zip format. Then log in to your WordPress dashboard and navigate to Plugins > Add New. You will be taken to the “Install Plugins” page.
By default, the Search tab will be displayed. Just switch to the Upload tab at the top of the page (right under “Install Plugins” and next to the Search tab).
You will see a screen like the one above. Click “Choose File” to browse the plugin zip file. Then click the “Install Now” Button.
After the successful installation of the plugin, you will be see a confirmation.
Click the “Activate Plugin” link to start using it on your blog. Note that you will need to adjust the plugin settings to your desired options.