If you have already downloaded the plugin file from a any website, you can upload it manually by following these steps:

1. Log in to your WordPress dashboard.
2. Navigate to “Plugins” in the left-hand menu and click on “Add New.”
3. Click on the “Upload Plugin” button at the top of the page.
4. Click on the “Choose File” button and select the plugin file from your computer.
5. Click the “Install Now” button to start the installation process.
6. Wait for the installation to complete, and then click the “Activate” button to enable the plugin.