Please refrain from making changes to the VM network settings. We will not be able to support you in case of further issues.
You can find all the instructions to set-up the VirtualBox for Decisioning and Pega Marketing courses in the Exercise System Guide attached in the same course. You'll only have to set-up the network adaptor settings at the VirtualBox level, and the VM will pick it up.
There are many threads in this forum where common issues (and resolutions) related to the exercise system are discussed. You might find them helpful. Here's one of them: