If it's an Oxwall plugin, there are a few ways to install easily, especially if you have FTP configured in Oxwall:

https://www.fastcomet.com/tutorials/oxwall/plugin-installation

I recommend using Filezilla to transfer the plugin over SFTP to your ow_plugins directory if you don't have the FTP settings configured / enabled.

To do it manually, you transfer the zip over to the ow_plugins directory and unzip it, then go to admin/plugins and install it from Available Plugins.

Ok Thanks