Manual Upload via WordPress Admin

If you have a copy of the plugin as a zip file, you can manually upload it and install it through the Plugins admin screen.

1. Navigate to Plugins > Add New.
2. Click the Upload Plugin button at the top of the screen.
3. Select the zip file from your local filesystem.
4. Click the Install Now button.
5. When installation is complete, you’ll see “Plugin installed successfully.” Click the Activate Plugin button at the bottom of the page.

Original article: https://wordpress.org/support/article/managing-plugins/#manual-upload-via-wordpress-admin