You need to incorporate the package
menu - software - master repository
the package is downloaded .zip (VSE880LMLRP6.ZIP)
So you did the right thing: check in the extension under extensions. But you also need to checkin the vse880lmlrp6.zip into the master repository.
If you have credential for the remote systems, you can push the agent from ePO. Under system tree, new system. If not, you can download the install package from there also using the option for that: system tree, actions, new systems, create and download agent installation package.
Once the management agent is installed, it will run under the system context and will communicate with ePO to receive tasks and policies. Create a task in ePO to deploy virusscan to all your managed devices in ePO. System tree, Assigned client task.
So that is the quick answer.
I would suggest you grab the manual for ePO to understand all those concepts. Also, you might not want to hear this, but ePO 4.6.x is end of life, you need ePO 5.3.x or 5.1.x